Preheat oven to 325°F (162°C). Line a 12-cup muffin tin with paper liners.

In a small bowl, combine the Oreo cookie crumbs and melted butter. Mix until well combined. Divide the mixture evenly among the cupcake liners and press firmly into the bottoms to form a crust.

Bake the crusts for 5 minutes. Remove from the oven and let cool while you prepare the filling.

Reduce oven temperature to 300°F (148°C).

In a large bowl, beat the cream cheese, sugar, and cocoa powder on low speed until smooth and well combined. Scrape down the sides of the bowl as needed. Be careful not to overmix.

Add the sour cream and vanilla extract. Beat on low speed until just combined.

Gradually add the Irish Cream Liqueur and beat on low speed until incorporated.

Add the eggs one at a time, beating on low speed after each addition until just combined. Scrape down the sides of the bowl after each egg.

Divide the batter evenly among the prepared cupcake liners, filling them about two-thirds of the way full.

Bake for 12 minutes. Then, turn off the oven and leave the oven door closed for an additional 8 minutes. The edges should be set, but the centers may still jiggle slightly.

Crack the oven door open slightly and allow the mini cheesecakes to cool in the oven for 15-20 minutes. Then, remove from the oven and let them cool completely on a wire rack. Chill in the refrigerator for at least 2 hours.

In a large mixing bowl, whip the cold heavy whipping cream on high speed until it begins to thicken.

Add the powdered sugar and Irish Cream Liqueur. Continue to whip on high speed until stiff peaks form.

Pipe or spoon the Baileys whipped cream onto each chilled mini cheesecake. Drizzle with extra Irish Cream or chocolate sauce, if desired.

Refrigerate until ready to serve. Store in an airtight container in the refrigerator for up to 4-5 days.