Preheat your oven to 350°F (175°C) and prepare two 8 or 9-inch round cake pans by greasing and flouring them or lining with parchment paper.

In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, baking powder, and salt.

In a separate medium bowl, whisk together the buttermilk, vegetable oil, eggs, and vanilla extract.

Pour the wet ingredients into the dry ingredients, mixing on low speed with an electric mixer until just combined.

Gradually add the hot water or coffee, mixing until the batter is smooth; note that the batter will be thin.

Divide the batter evenly between the prepared cake pans and bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.

Let the cakes cool in the pans for 10 minutes before inverting them onto a wire rack to cool completely.

While the cakes cool, beat the softened butter in a large bowl with an electric mixer until light and fluffy.

Gradually add the sifted powdered sugar, alternating with milk or cream, beating until smooth and creamy.

Stir in the vanilla extract.

Crush 20-25 Oreo cookies in a Ziploc bag with a rolling pin until you have a mix of fine crumbs and small chunks.

Fold the crushed Oreos into the buttercream.

Once the cakes are completely cool, place one layer on your serving plate and spread about one-third of the Oreo buttercream evenly over the top.

Place the second cake layer on top and frost the top and sides of the entire cake with the remaining buttercream.

Decorate the cake with additional crushed Oreos or whole cookies if desired.