Set the oven temperature to 350℉ before using. Prepare two baking sheets by lining them with parchment paper or silicone baking mats. Set them aside.

Combine the cake mix, eggs, and vegetable oil in a large bowl and beat until the mixture is smooth and well incorporated, which should take approximately 2 minutes.

Put the confectioner's sugar in a small bowl.

Portion out the cookie batter using a 1 ½ Tablespoon cookie scoop and coat the cookie dough balls entirely with confectioner's sugar by rolling them in it.

Ensure that the coated cookie dough balls are placed with a minimum distance of 3" between them on the prepared cookie sheets.

Bake until lightly golden and spread out, typically for 10-12 minutes.

After using a teaspoon measuring spoon to press into the center of each cookie and create an indent, let them cool for 5 minutes.

While doing that, heat the white chocolate chips in a microwave-safe bowl in 30-second intervals, making sure to stir thoroughly after each heating to prevent the chocolate from burning. If the chocolate is too stiff, you can add coconut oil or shortening if desired.

Distribute about 1 teaspoon of melted white chocolate into the hollow of every thumbprint cookie.