Preheat oven to 350°F (175°C). Butter and flour two 8 or 9-inch round cake pans.

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

In a separate bowl or measuring cup, whisk together hot water, coffee, oil, vinegar, and vanilla extract.

Slowly add the wet ingredients to the dry ingredients, mixing until smooth.

Pour batter evenly into the prepared pans. Bake for 34-38 minutes, or until a toothpick inserted into the center comes out clean.

Let the cakes cool completely before removing from the pans and frosting.

In a large bowl, beat butter and shortening with a hand mixer until smooth. Mix in marshmallow cream until smooth.

Slowly mix in powdered sugar, then add salt, vanilla, and 1 tablespoon of cream. Mix on medium speed until smooth, adding more cream as needed for consistency.

Taste and add more salt if the frosting is too sweet.

Remove cake layers from pans and level as needed. Place one cake layer on a serving plate.

Top with half of the frosting and smooth it to the edges. Sprinkle with half of the crushed Oreos.

Add the second cake layer and repeat with frosting and crushed Oreos.

Serve at room temperature. Store loosely covered in the refrigerator.