Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a large mixing bowl, combine the flour, sugar, cocoa powder, baking powder, baking soda, and salt. Mix well.
Add the eggs, milk, vegetable oil, and vanilla extract to the dry ingredients. Beat with an electric mixer on medium speed until well combined.
Carefully stir in the boiling water until the batter is smooth; it's okay if it’s thin.
Pour the batter onto the prepared baking sheets, spreading it evenly. Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted into the center comes out clean.
Remove from the oven and allow the cakes to cool in the pans for 10 minutes. Then, transfer them to a wire rack to cool completely.
While cooling, prepare the cream filling. In a small bowl, whip the heavy cream, powdered sugar, and vanilla extract until soft peaks form. If desired, add cocoa powder to flavor the cream.
Once the cakes are completely cooled, spread a generous layer of cream filling on the bottom side of half of the cakes. Top with the remaining cakes to create sandwiches.
For the ganache, heat the heavy cream in a small saucepan until it’s just about to boil. Remove from heat and add the chocolate chips. Stir until melted and smooth.
Drizzle or dip the tops of the snack cakes in the chocolate ganache. Let them set for a few minutes.