Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large mixing bowl, sift together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add the eggs, milk, vegetable oil, and vanilla extract to the dry ingredients. Beat on medium speed until well combined, about 2 minutes.
Carefully stir in the boiling water. The batter will be thin; this is normal.
Divide the batter evenly between the prepared cake pans.
Bake for 30 to 35 minutes or until a toothpick inserted into the center comes out clean.
Remove the cakes from the oven and allow them to cool in the pans for 10 minutes.
Turn the cakes out onto a wire rack and cool completely before frosting.
To prepare the frosting, beat the softened butter on medium speed until creamy, about 2 minutes.
Gradually add the powdered sugar and cocoa powder, beating on low speed until combined.
Add salt, vanilla extract, and heavy cream. Beat on high speed for 3 minutes until light and fluffy.
Place one cake layer on a serving plate. Spread a thick layer of frosting on top.
Place the second cake layer on top and frost the top and sides of the cake evenly.
Decorate the cake with colorful Easter-themed sprinkles.
Refrigerate the cake for at least 30 minutes before serving to set the frosting.