This light and flavorful cake uses an unusual flour, tempers that flour's occasional bad behavior with ingredients rarely encountered in sponge cakes, then uses traditional methods to produce an exceptionally tender, moist and fragrant dessert. A lemon buttercream frosting caps this delightful creation.
The key to achieving this cake's elegant tenderness is technique, specifically in the way the eggs are whipped. Pay close attention to temperature and process, using an instant-read thermometer if you have one. Pre-warming the eggs in a hot water bath is critical to success.
Yield: One, 6-inch diameter cake. (For a 9-inch cake, double all ingredients.)
Time to make: 1 hour active and 30 - 35 minutes oven dwell.
Tools needed: Stand mixer with whisk attachment. Saucepan large enough to hold stand mixer bowl. 3 medium bowls. Instant read thermometer. Hand mixer with whisk beaters . Metal, 6-inch circular cake pan. Bakers parchment. Measuring cups and spoons and/or kitchen scale. Whisk.
1) Heat oven to 350. Place eggs, in their shells, in a medium bowl and fill the bowl with water at 100 F (body temperature), allowing them to warm while you measure ingredients and set up. Lightly grease the inside of a 6" circular cake pan and line with bakers parchment, making sure parchment along the sides is at least 1 inch taller than cake pan. Do not grease the parchment. Place bowl of stand mixer in a large sauce pan and add enough water to saucepan to reach to within 1 inch of the saucepan rim. Remove mixer bowl and place saucepan over low heat.
2) Place the "additional" 1 Tablespoon of sugar, the millet flour, the salt, and the baking powder in one of the medium bowls. Whisk to combine.
3) In a third medium bowl, whip the cream and the honey with a hand mixer until soft peaks form, about 3 minutes. Add the lemon juice and whip again to assure stability.
4) Measure sugar into bowl of the stand mixer. Add the eggs and the yolk. Place the mixer base into the water simmering on the stove. Hand-whisk eggs and sugar together, occasionally dipping instant read thermometer or a finger into the mix. Stir until 100 F is reached (body temperature). Lift stand mixer bowl from water, turn off heat, allow mixer bowl to drain, then move to mixer base. Using the whisk attachment, whip eggs on high for 2- 5 minutes, until they have become pale, foamy, and risen. Reduce speed of mixer to medium and continue to beat 12 - 17 more minutes. When eggs have tripled in volume, are glossy, and noticeably stiffer, with ridges forming behind the whisk wires, stop mixer and remove bowl.
5) Gently fold flour blend into eggs, taking care to minimize egg collapse (there will be some). Remove 1/2 cup batter and whip into the whipped cream. Gently fold whipped cream into eggs (watch closely - they are the exact same color). Pour batter into prepared cake pan. Bake about 35 minutes, or until an inserted toothpick comes out clean. NOTE: Do not open oven to check cake until at least 30 minutes or center may collapse.
6) Remove cake to a cooling rack. After five minutes, run a knife around the inside of the pan between parchment and pan to prevent sticking. Allow cake to cool an hour, then invert to remove from pan. Place a flat plate on the bottom of the cake and re-invert and allow to finish cooling completely.
7) To frost, slice the cake evenly in half. Using the stand mixer with whisk, add butter, the confectioners sugar and the lemon zest. Start mixer on low to blend all ingredients, then increase speed to medium-high. Once frosting begins to fluff, drizzle in the lemon juice, reserving 1 Tablespoon. Taste frosting. If it needs richness, add heavy cream, 1 teaspoon at a time, while whipping. If it needs tartness, add lemon juice while whipping. If it's just right, spread half on the bottom half of the cake. Carefully position top half on the frosted bottom half and frost the top of your cake, and BINGO! You're ready for a celebration!