London Fog Cake made with Toasted Sugar

Recipe adapted from Serious Eats (seriouseats.com)

Ingredients

For the cake:

• 16 oz toasted sugar (about 2 1/4 cups; 455g)**
• 4 1/2 tsp baking powder
• 2 tsp (8g) Diamond Crystal kosher salt
• 8 oz unsalted butter (16 Tbsp; 225g), soft but cool, about 60°F (16°C)
• 3 large eggs, brought to about 65°F (18°C)
• 1/2 oz vanilla extract (about 1 Tbsp; 15g)
• 16 oz whole milk (about 2 cups; 455g), brought to about 65°F (18°C)
• 3 bags of Earl Grey black tea
• 16 oz all-purpose flour (about 3 1/2 cups, spooned; 455g)

For the Swiss meringue buttercream:

• 6 oz egg whites (2/3 cup; 170g), from 5 to 6 large eggs
• 11 oz plain or toasted sugar (about 1 2/3 cups; 310g)
• 3/4 tsp (3g) Diamond Crystal kosher salt
• 1/4 tsp cream of tartar
• Scraped seeds from 1 split vanilla bean (optional)
• 20 oz unsalted butter (5 sticks; 565g), softened to about 65°F (18°C)
• 1 tsp (5ml) vanilla extract

For the lemon drip icing (optional):

• ½ cup heavy whipping cream
• ½ cup white chocolate, chopped
• 2 Tbsp Limoncello

Directions

For the cake:

1. Adjust oven rack to lower-middle position and preheat to 350°F (180°C). Lightly grease 2 7-inch anodized aluminum cake pans and line with parchment. Lightly grease 1 6-cup bundt pan (recipe also works for 3 8-inch cake pans).
2. In a saucepan, heat milk on medium heat until it steams and just starts to bubble bu isn’t boiling. Remove from heat. Add tea bags and steep for 3 minutes. Remove tea bags and allow milk to cool to room temperature (or refrigerate if not using immediately).
3. In the bowl of a stand mixer fitted with the paddle attachment, combine sugar, baking powder, salt, and butter. Mix on low speed to roughly incorporate, then increase to medium and beat until fluffy and light, about 5 minutes. About halfway through, pause to scrape the bowl and beater with a flexible spatula.
4. With the mixer still running, add the eggs one at a time, letting each fully incorporate before adding the next, then dribble in the vanilla. Reduce speed to low and sprinkle in about 1/3 of the flour, then drizzle in 1/3 of the Earl Grey-infused milk. Repeat with remaining flour and milk, working in thirds as before.
5. Scrape the bowl and beater with a flexible spatula, and resume mixing on medium speed for about 3 seconds to ensure everything is well combined. The batter should look creamy and thick, registering between 65 and 68°F (18 and 20°C) on a digital thermometer. (Significant deviation indicates ingredients were too warm or too cold, which can lead to textural problems with the cake.)
6. Fold batter once or twice from the bottom up with a flexible spatula, then divide evenly between prepared cake pans (about 20 ounces or 565g if you have a scale). Stagger pans together on the oven rack, and bake until puffed, firm, and pale gold, about 32 minutes. If your oven has very uneven heat, pause to rotate the pans after about 20 minutes. Alternatively, bake two layers at once and finish the third when they’re done.
7. Cool cakes directly in their pans for 1 hour, then run a butter knife around the edges to loosen. Invert onto a wire rack, peel off the parchment, and return cakes right-side up (covered in plastic, the cakes can be left at room temperature for a few hours).
8. Prepare the buttercream.

For the buttercream:

1. Fill a wide pot with at least 1 1/2 inches of water, with a thick ring of crumpled tinfoil placed on the bottom to act as a “booster seat” that will prevent the bowl from touching the bottom of the pot. Place over high heat until steaming-hot, then adjust temperature to maintain a gentle simmer. Combine egg whites, sugar, salt, cream of tartar, and vanilla seeds (if using) in the bowl of a stand mixer. Set over steaming water, stirring and scraping constantly with a flexible spatula, until egg whites hold steady at 185°F (85°C). This should take only 10 to 12 minutes, so if mixture seems to be moving slowly, simply turn up the heat. Once ready, transfer to a stand mixer fitted with a whisk attachment and whip at high speed about 10 minutes, until meringue is glossy, stiff, and cool to the touch, around 90°F (32°C).
2. With mixer still running, add butter, 1 or 2 tablespoons at a time. Initially, the volume of the meringue will decrease dramatically; it may even seem soupy along the way, but as the cool butter is added, the mixture will begin to thicken and cool. In the end, buttercream should be thick, creamy, and soft but not runny, around 72°F (22°C). Mix in vanilla extract on low speed until well combined.
3. Use buttercream right away, or transfer to a large zipper-lock bag, press out the air, and seal. Buttercream can be refrigerated for up to 2 weeks and frozen for up to several months. (The main issue with longer storage in the freezer is odor absorption, not spoilage.) Rewarm to 72°F and re-whip before using.
4. Troubleshooting: If warmer than 74°F (23°C), the buttercream will be soft and loose; pop it in the fridge for 15 minutes and re-whip to help it thicken and cool. If colder than 68°F (20°C), the buttercream will be firm and dense, making it difficult to spread over cakes and slow to melt on the tongue, creating a greasy mouthfeel; to warm, briefly set over a pan of steaming water, just until you see the edges melting slightly, then re-whip to help it soften and warm. Full troubleshooting guide and video here.

For the drip icing:

1. In a small pot, heat the cream until just warm.
2. Reduce the heat and add in the white chocolate. Mix until the chocolate is completely melted.
3. Remove from the heat and place in a container. Stir in limoncello.
4. Cool completely and cover.

Assembling the cake:

1. Using a serrated bread knife, trim the top of the two round cakes to make them even.
2. On a cake stand or plate, place a small amount of icing in the center (to keep the cake from moving around on the stand). Place the first cake layer on the stand and spread about 1 cup of the buttercream evenly on the top surface. Place the second layer and repeat.
3. With an offset spatula, spread an even layer around the outside of the cake, leaving some portions of the cake exposed. Play around with it until you get the look you would like. Place the top bundt layer and chill entire cake in the freezer for 15 minutes.
4. Take the cake out of the freezer and slowly start to spoon the drip icing over the top of the cake. It will start to run down the sides but will seize up due to the temperature of the cake.
5. Keep the cake refrigerated for up to two days. Take it out of the fridge at least 2 hours prior to serving.

**For the toasted sugar:

1. Adjust oven rack to center position and preheat oven to 300°F. Pour 4 pounds (9 cups; 1.8kg) granulated white sugar into a 9- by 13-inch glass or ceramic baking dish. Toast until the sugar turns ivory, about 1 hour.
2. Stir thoroughly and continue roasting, pausing to stir every 30 minutes. The sugar will produce steam as a byproduct of toasting, so it must be stirred well to allow that moisture to escape. Stirring should also help move hot sugar from the edges toward the center, and cool sugar from the center toward the edges, for even toasting. Continue toasting and stirring every 30 minutes until the sugar has darkened to the desired degree, from a light beige to the color of traditional brown sugar, between 2 and 4 hours more.
3. When the sugar has finished toasting, set aside and cool to room temperature, stirring from time to time to speed the process and allow for continued evaporation of steam. Alternatively, the cooling process can be sped along by pouring the sugar into a large, heat safe container. Once fully cool, transfer to an airtight container and store as you would plain white sugar. It can be used interchangeably, by weight or volume, in any recipe that calls for white sugar.
4. Troubleshooting: In an oven that runs hot, or when using a different volume of sugar, or a different size baking dish, or a metal dish, the sugar will heat more rapidly, and may begin to liquify much sooner than expected. If this happens, immediately pour the dry sugar into a large stainless steel bowl, leaving the melted caramel behind. If the sugar is not stirred thoroughly throughout the toasting process, it may clump severely along the way and as it cools; should this happen, grind the cooled sugar in a food processor until powdery and fine.

Enjoy!