Preheat the oven to 350°F. Line two 6-inch round cake pans with parchment paper rounds on the bottoms and set them aside. In a small bowl, combine the flour, baking powder, and salt; stir well and set aside. In a small pot or microwave-safe bowl, combine the butter, milk, oil, and vanilla extract, heating gently on the stovetop or in the microwave just until the butter melts—do not let it boil. Remove from heat and cover to keep warm while preparing the batter. In a large mixing bowl, beat the eggs and sugar with an electric hand mixer fitted with a whisk attachment on medium speed for 6 minutes or until the mixture triples in size and turns very pale, nearly white. Add half of the flour mixture to the eggs and sugar, mixing on low speed until just combined. Add the remaining flour mixture and mix again until mostly combined—some small flour patches are fine as overmixing is to be avoided. With the mixer still on low, gradually pour in the warm milk mixture, mixing until the batter is smooth and fluid. Divide the batter evenly between the prepared pans, filling each about halfway. Bake for 35–40 minutes, or until a toothpick inserted into the center comes out mostly clean with a few moist crumbs. Let the cakes cool in the pans for 15 minutes, then run an offset spatula around the edges and transfer them to a wire rack to cool completely.

In a large bowl, combine the cold whipping cream, powdered sugar, and vanilla extract. Using a hand mixer with a whisk attachment, beat the cream until it forms soft peaks. Scoop out a small portion of the whipped cream into a separate bowl and set aside. Continue beating the remaining cream until firm peaks form. To the reserved whipped cream, add the cocoa powder and mix until evenly tinted brown. Transfer this chocolate whipped cream into a small piping bag and snip off the tip; set aside. Transfer both the plain whipped cream and the chocolate whipped cream into separate piping bags and cut the tips off.

Place one cake layer on a large serving plate or cake board. Pipe dollops of plain whipped cream around the edge of the cake, extending towards the center, then use a spatula to gently smear the tails of the dollops inward. Spoon the strawberry jam into the center of the cake and smooth it out evenly with an offset spatula, taking care not to disturb the whipped cream border. Place the second cake layer on top, then pipe additional dollops of whipped cream over the top. Arrange halved fresh strawberries on the whipped cream and insert a birthday candle in the center. Using the chocolate whipped cream, pipe small “legs” extending out from the bottom cake layer onto the plate. Melt the chopped dark chocolate either in the microwave or on the stovetop, transfer the melted chocolate into a small piping bag, and snip off the tip. Pipe eyes and a smile onto the bottom cake layer between the chocolate whipped cream legs to complete the decoration.