Preheat the oven to 350°F. Line a muffin tin with cupcake liners. Set aside.
Add about an inch of water into a small saucepan. Heat the water over medium-high until the water begins to boil. Turn off the heat, but leave the saucepan on the stove. Place a larger heatproof bowl over the saucepan – ensure it is large enough that it doesn’t touch the water below.
Add the chocolate and butter to the bowl and stir as it melts. Once the butter and chocolate are melted and well-mixed and incorporated, add the oil and sugar then remove the bowl from the saucepan. Mix well and allow the ingredients to cool slightly.
Beat in the eggs until well incorporated.
Mix in the cocoa powder, flour, and baking powder. Mix in well. Add the milk and stir until combined.
Evenly divide the batter among the cupcake liners and bake for 15 – 18 minutes, or until a toothpick comes out with a few crumbs clinging to it.
Allow the muffins to cool completely.
As the muffins are cooling, beat the heavy cream until medium peaks form. Beat in the cocoa powder, powdered sugar, and vanilla. Fit a piping tip with your favorite tip and fill with the whipped cream. Pipe the cream on the cooled muffins.