Line a muffin tin with paper cupcake liners (or use a silicone pan, which is recommended)
Finely crush 45 Oreo's in a food processor or blender. Reserve ¼ cup of Oreo crumbs to top the dirt cups.
Pour the crushed Oreo's into a mixing bowl and add melted butter. Mix until the butter is fully incorporated into the Oreo crumbs.
Place two heaping tablespoons of crust mixture into each muffin tin and use your fingertips to firmly press the mixture throughout the muffin tin (making sure to press it up the sides as well).
Place the filled muffin tin in the fridge for at least 30 minutes or in the freezer for 15 minutes to set the crust.