Preheat oven to 350°F.
Mix cake mix, whisked eggs, and melted butter in a large bowl until fully combined. Dough will be thick.
Using a medium cookie scoop or tablespoon, drop dough onto parchment-lined baking sheets.
Bake for 7-8 minutes until lightly golden. Cool on baking sheet for 4-5 minutes before transferring to a rack.
For the glaze, combine butter, sugar, water, and vanilla in a saucepan over medium-low heat. Cook until sugar dissolves, whisking constantly.
Spoon glaze over cooled cookies and let set. Dust with powdered sugar if desired.
Notes
Experiment with different cake mix flavors for unique variations.
Store cookies in an airtight container for up to 3 days at room temperature.