1/4 cup unsalted butter at room temperature plus more for pan 1/2 cup packed light brown sugar 1/2 cup granulated sugar 1 large egg 1 teaspoon vanilla extract 1 cup all - purpose flour 1 teaspoon baking powder 1 teaspoon fine sea salt 1-1/2 cups
mix - ins (
assorted chocolate chips, pretzels,
nuts, crushed potato chips, dried fruit, shredded coconut)