Cake with a surprise letter

Ingredients:

Cake

• Cooking spray
• 330 g unsalted butter at room temperature
• 3 tbsp. sugar
• 7 large eggs at room temperature
• 1 tsp vanilla extract
• 4.5 cups premium flour
• 1 teaspoon of salt
• 1 tbsp baking powder salt
• 1 cup low-fat yogurt or kefir
• 3-4 drops of green food coloring (or any other color)

Swiss meringue

• Whites of 10 eggs
• 2 tbsp. sugar
• A pinch of salt
• Special equipment: 12-cup round cake tin with a hole in the center, 5cm D-shaped cookie cutter.

Preparation:

1. Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper and spray with cooking spray. Spray a cake pan with cooking spray.
2. Cake:
   
   In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugar until light and fluffy, about 5-10 minutes, stopping several times to scrape down the sides of the bowl. Add the eggs one at a time, beating for 30 seconds after each addition. Stir in the vanilla extract.
3. In a large bowl, whisk together the flour, salt, and baking powder for 30 seconds to disperse the baking powder. With the mixer running on low speed, alternately add the flour mixture and the soured milk. Mix thoroughly with a silicone spatula.
4. Transfer a generous portion of the batter (a quarter or a third) to a bowl. Add green food coloring and stir until the batter is evenly colored. Transfer the green batter to the prepared baking sheet and bake until the crust is cooked through and set, 10-15 minutes. Let cool, then freeze for 20-30 minutes.
5. Spread one-third of the uncolored dough in the bottom of the prepared cake pan. Cut out 14-15 D-shaped letters (or other shapes) from the green cake core. Place the letters upside down in the pan, with the straight sides facing the center. Don't press the letters completely into the dough; just enough so they stand upright. Place the letters as close together as possible while maintaining the correct angle.
   
   Note
   
   If you have shapes or letters with an open center, it's best to apply a little dough to the open area before placing the shapes in the mold.
6. Fill a large pastry bag with the remaining uncolored batter and pipe it into the pan, making sure to fill all corners and completely cover the letters. Bake until the cake is golden brown and springs back when lightly pressed, 50-60 minutes. Let cool completely in the pan.
7. Swiss meringue:
   
   In the bowl of a stand mixer, combine the egg whites, sugar, and salt. Place the bowl over a medium saucepan of simmering water, making sure the water doesn't touch the bottom of the bowl (the whites should be heated in a double boiler). Whisking constantly, heat the egg white mixture until the sugar is completely dissolved and the meringue is hot to the touch. If you're concerned about raw eggs, check the temperature of the meringue; it should be at least 160°F (76°C). Transfer the bowl to the stand mixer and beat the meringue on high speed until stiff, glossy peaks form, or until the meringue reaches room temperature, about 10 minutes.
8. Assembly:
   
   Run a long, thin knife around the edge of the pan to loosen the cake. Place the cake plate face down on the cake and invert the pan. Carefully lift the pan, leaving the cake on the plate. Spread an even layer of Swiss meringue over the cake. Serve immediately or refrigerate.