Begin by setting the oven to 350°F (175°C), then prepare two 8-inch round cake pans. 

Lightly grease and flour them, then add a round of parchment paper to the bottom of each, this makes removing the cake layers super easy later on.

In a large mixing bowl, whisk together the white cake mix, sugar, and flour until well combined. 

Then add in the milk, sour cream, oil, eggs, and vanilla extract. Begin on low speed to blend the ingredients, then switch to medium and continue mixing for around 2 minutes, until the batter is smooth and airy.

Split the batter evenly between the prepared pans and bake for 25 to 30 minutes, until a toothpick inserted in the center comes out mostly clean. After baking, cool the cakes entirely 

While the cakes are cooling, prepare the vanilla filling. In a mixing bowl, combine the instant vanilla pudding mix with heavy cream and whisk until smooth. 

Start slowly, then increase to medium-high speed until it thickens into a light and fluffy cream. If it feels a bit too thick, just stir in a splash of extra cream to loosen it up a little.

For the ganache, place the chocolate chips in a microwave-safe bowl and pour the heavy cream on top. 

Microwave for 30 seconds, stir, and repeat once more if needed until the chocolate is nearly melted. Let it sit for a minute, then stir until silky smooth. 

Let the ganache cool for about 10 minutes, it should thicken slightly but still be pourable.

Begin assembly by placing one cake layer on a serving dish, then smooth the vanilla filling on top. 

Gently layer the second cake over it to finish the stack. 

Then pour the ganache right in the center of the cake and guide it toward the edges, letting it drip slightly down the sides for that signature look.

And that’s it, your Boston Cream Pie is ready to wow!