Preheat your oven to 350°F (175°C) and prepare your cupcake pan with paper liners.

In a large mixing bowl, cream the softened butter, coconut or vegetable oil, and granulated sugar together until light and fluffy.

Add the egg whites one at a time, mixing well after each addition until smooth and homogenous.

Mix in the sour cream, milk, and vanilla extract until well combined.

Sift together the gluten-free flour, baking powder, and salt, then gradually add to the wet ingredients until just combined.

Fold in the crushed gluten-free chocolate sandwich cookies gently to distribute without over-mixing.

Place one chocolate sandwich cookie at the bottom of each cupcake liner.

Fill each cupcake liner about three-quarters full with the batter.

Bake for approximately 22 minutes or until a toothpick inserted comes out clean.

Cool the cupcakes in the pan for 10 minutes before transferring them to a wire rack to cool completely.

Beat the softened butter and cream cheese together until creamy and well-combined.

Gradually mix in the powdered sugar, followed by the vanilla extract and heavy cream until light and fluffy.

Frost the cooled cupcakes generously with the frosting, using a knife or piping bag to create swirls.