Step 1: Prepare the Cake

1. Preheat oven to 350°F (175°C). Grease a mini muffin tin or line with paper liners.
2. Mix dry ingredients: In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, and salt.
3. Combine wet ingredients: In another bowl, mix warm water, oil, vinegar, and vanilla.
4. Make batter: Pour wet ingredients into dry ingredients and stir until just combined. Fold in crushed Oreos.
5. Bake: Fill mini muffin cups ¾ full. Bake for 15-18 minutes or until a toothpick comes out clean.
6. Cool completely on a wire rack.

Step 2: Make the Truffle Filling

1. Heat cream: In a small saucepan, heat heavy cream until it just begins to simmer.
2. Melt chocolate: Pour hot cream over chopped chocolate in a bowl. Let sit for 2 minutes, then stir until smooth.
3. Add cream cheese: Beat in softened cream cheese and powdered sugar until smooth.
4. Fold in Oreos: Gently fold in crushed Oreo cookies.
5. Chill: Refrigerate for 30 minutes until slightly firm.

Step 3: Assemble the Cakes

1. Hollow out cakes: Using a small spoon or melon baller, carefully remove the center of each mini cake, leaving walls and bottom intact.
2. Fill: Spoon or pipe the truffle filling into each hollowed cake.
3. Level: Smooth the top with a knife.

Step 4: Make the Ganache

1. Heat cream: Warm heavy cream in a saucepan until simmering.
2. Make ganache: Pour over chopped chocolate and butter. Stir until smooth and glossy.
3. Cool slightly: Let cool for 5 minutes until slightly thickened.

Step 5: Final Assembly

1. Glaze: Dip the top of each cake into the ganache or spoon it over.
2. Decorate: Top each cake with a mini Oreo cookie while ganache is still wet.
3. Garnish: Add chocolate shavings if desired.
4. Set: Refrigerate for 15 minutes to set the ganache.