Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.

In a large mixing bowl, whisk together the flour, granulated sugar, cocoa powder, baking powder, and salt until well combined.

Add the milk, vegetable oil, eggs, and 2 teaspoons of vanilla extract to the dry ingredients. Mix until smooth.

Gradually stir in the boiling water until the batter is well combined (the batter will be thin). Pour the batter into the prepared baking pan.

In a separate bowl, mix the ricotta cheese, powdered sugar, lemon zest, and 1 teaspoon of vanilla extract until smooth.

Carefully spoon the ricotta mixture over the chocolate batter in the baking pan. Do not mix; it will sink during baking.

Bake for 40-45 minutes or until a toothpick inserted in the center comes out clean. Allow the cake to cool completely in the pan.

In a medium bowl, whip the heavy cream with 2 tablespoons of powdered sugar until stiff peaks form.

Once the cake is cool, spread the whipped cream over the top of the cake. Garnish with chocolate shavings or a dusting of cocoa powder if desired.

Slice and serve. For best flavor, chill the cake in the refrigerator for at least 1 hour before serving.