Preheat your oven to 325°F (160°C) and prepare a mini muffin pan by greasing it lightly.

In a large mixing bowl, whisk together your chosen cake mix and flour until blended. Add melted butter, egg, egg yolk, and vanilla extract, and stir until cohesive.

Scoop portions of dough and roll into balls, then coat in granulated sugar before placing them in the muffin pan.

Bake for 14 minutes, or until puffy and starting to crack on the surface.

Press an indent in the center of each cookie cup using the handle of a wooden spoon immediately after removing from the oven.

Allow the cookie cups to cool in the pan for 5-10 minutes before transferring to a wire rack.

In a microwave-safe bowl, combine white chocolate chips and heavy cream. Microwave in 15-second intervals, stirring, until smooth.

Carefully fill each cookie cup with the ganache, mounding slightly in the center.

Decorate each with colorful pastel M&Ms, placing one in the center and two above for ears.

Allow the filled cookie cups to sit at room temperature for about 2 hours to let the ganache firm up.