Brooklyn Blackout Cakelets

Ingredients

• 1/2 cup all purpose flour
• 1/3 cup natural cocoa powder
• 1/2 teaspoon baking powder
• 1/2 teaspoon baking soda
• 1/3 teaspoon kosher salt
• 2/3 cups sugar
• 1 large egg
• 1/2 large egg yolk
• 1/3 cup buttermilk
• 1.3 oz unsalted butter, melted
• 1 teaspoon vanilla extract
• 1/3 cup hot coffee
• 1 large egg yolks
• 1 1/2 oz sugar
• 2 tsp cornstarch
• 1 pinch kosher salt
• 1/3 cup water
• 3 Tbsp + 2 tsp heavy cream
• 1 ounce semisweet chocolate, finely chopped (I used chips)
• 1/3 teaspoon vanilla extract
• 1.3 oz unsweetened chocolate, coarsely chopped
• 1.84 oz unsalted butter, softened
• 2 1/2 oz powdered sugar
• milk, as needed, to thin the frosting (optional)