Make the cupcake batter. Sift flour, baking powder, baking soda and salt in a medium bowl and whisk to blend evenly.

Combine soft butter with sugar in a large bowl and mix using an electric hand mixer on medium-high speed for about 2 minutes until very pale, creamy and fluffy. Add egg and mix until well incorporated and smooth, but do not over-mix at this stage or the batter will develop large air bubbles. Scrape down the sides and around the bottom of the bow. Mix in oil, vanilla and sour cream.

Place the milk in a heatproof jug and warm it slightly in the microwave for about 25 seconds. It should feel warm to the touch, but it should not simmer.

Add one third of the flour mixture to the butter mixture and mix on medium-low speed until mostly incorporated. Add half of the milk and mix until well blended, about 10-15 seconds. Mix in half of the remaining flour mixture followed by the last of the milk on medium speed just until the batter is smooth. Scrape around the bowl to incorporate everything evenly, then finally mix in the rest of the flour mixture on low speed until evenly combined. Then, just when the flour is combined, increase the speed to medium-high and mix for 5-10 seconds to emulsify the batter. Use a wide spatula to fold the batter with a few strokes to help deflate any large air pockets.

Divide the batter evenly among paper cups, filling them about two-thirds full. Do not over-fill or the batter will flow over as it rises. Tap the pan on the counter top several times to help knock out any large air bubbles. Bake for 17-20 minutes until just lightly golden and a toothpick inserted into the center comes out clean. Remove from oven, let cool for 1 minute in the pan and then transfer them individually to a wire rack to cool completely.

Make the ganache filling. Place finely chopped chocolate and cream in a heatproof bowl and set it over a saucepan of simmering water. Whisk gently and constantly just until chocolate is completely melted and smooth. Remove from heat and stir in vanilla bean paste and crushed Oreo. Place it in the fridge to thicken for about an hour until it reaches a spreadable consistency.

Assemble cupcakes. Use a small paring knife to cut out the center of each cupcake. Fill it with about a heaped teaspoon of the ganache filling and then replace the cut-out. Spread or pipe the frosting over top and decorate with an Oreo cookie or more cookie crumbs if desired.