Preheat oven to 350°F (175°C). Grease and flour two 8-inch round cake pans and line with parchment paper.

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

Whisk in eggs, milk, oil, and vanilla extract until smooth.

Pour in hot coffee and mix until just combined (batter will be thin).

Fold in chopped Oreos gently.

Divide batter evenly between prepared pans.

Bake for 28–32 minutes, or until a toothpick inserted in the center comes out clean.

Cool cakes in pans for 10 minutes, then transfer to wire racks to cool completely.

Dissolve instant coffee granules in hot water; set aside to cool.

In a large bowl, beat butter on high speed until creamy and pale, about 3 minutes.

Gradually add powdered sugar, mixing on low and then on medium until fully combined.

Add dissolved coffee, heavy cream, and salt; beat until fluffy, 3–4 minutes.

Fold in finely crushed Oreos until just combined.

Place one cake layer on your serving plate. Spread a thick layer of buttercream over the top.

Top with the second cake layer and frost the top and sides generously.

Decorate with extra Oreo cookies as desired.

Slice and indulge!