Birthday cake on a baking sheet

Ingredients:

Cake

• 250 g unsalted butter, room temperature
• 3 tbsp. sugar
• 6 large eggs, room temperature
• 220 g (about 1 cup) sour cream, room temperature
• 1.5 tsp vanilla extract
• Zest of 1 lemon
• 3 cups premium flour
• 1/3 cup cornstarch
• 1 teaspoon coarse salt
• 1 teaspoon of baking soda

Glaze

• 700 g semi-sweet chocolate granules
• 1.5 cups heavy cream
• 2 tablespoons light corn syrup
• 0.5 tsp vanilla extract
• 55 g unsalted butter, room temperature
• Chocolate candies for decoration (recommended: M&M's)

Preparation:

1. Preheat oven to 175°C. Grease and flour a 30x45x4 cm baking pan.
2. Cake:
   
   In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugar on medium-high speed until light and fluffy, about 5 minutes. Reduce the mixer speed to medium and add the eggs, 2 at a time, then the sour cream, vanilla extract, and lemon zest, scraping down the sides of the bowl as needed. Mix well. Sift together the flour, cornstarch, salt, and baking soda. With the mixer on low speed, gradually add the flour mixture to the butter mixture, mixing just until the flour is evenly incorporated.
3. Then mix by hand until the dough is smooth. Transfer the dough to a baking sheet and spread it evenly. Smooth the surface with a spatula and bake on the middle rack of the oven for 25-30 minutes, or until a toothpick inserted into the center of the cake comes out clean. Cool the cake on the baking sheet to room temperature.
4. Glaze:
   
   Place the chocolate chips in a bowl, add the heavy cream, and place the bowl over a saucepan of simmering water. Stir until the chocolate is completely melted. Turn off the heat, add the corn syrup and vanilla extract, and let the chocolate mixture cool to room temperature. In the bowl of a stand mixer fitted with a whisk attachment, beat the chocolate mixture and softened butter on medium speed for a few minutes until the glaze thickens.
5. Spread the icing evenly over the cake. Decorate the cake with chocolate candies with the kids.