Step 1

Preheat oven to 350F. Line a baking sheet with parchment paper.

Step 2

In the bowl of a mixer fitted with a paddle attachment, cream together butter and sugar until light in color and fluffy. Add the egg and vanilla; mix well.

Step 3

In a separate bowl, sift together the flour, cocoa powder, baking soda and salt. Add the dry ingredients to the butter mixture and beat just until combined.

Step 4

Scoop rounded pingpong ball-sized balls of batter onto the prepared baking sheet. Bake for 9-11 minutes, until the centers no longer look wet. Let cool on baking sheet for a minute or 2 and then transfer to a wire rack to cool completely. Repeat with remaining batter.

Step 5

In a clean bowl, cream the butter until light and fluffy. Add the vanilla and mix well. Sift the cocoa powder and powdered sugar together; add to the butter in small batches and beat until all the sugar is incorporated. Add heavy cream 1 tablespoon at a time until your filling reaches desired consistency.

Step 6

When cakes are cool, spread a bit of the filling on half of them and then top with another cake.

Step 7

Microwave the chocolate and oil in 20 second bursts, stirring between each one, until the chocolate is melted. Drizzle over each cake. Let sit until chocolate is set.