In a large mixing bowl, cream together the butter and sugar using a hand mixer until light and fluffy, about 2-3 minutes. Beat in the egg and vanilla until fully combined.

In a separate bowl, whisk together the flour, baking powder, and salt. Gradually fold this mixture into the wet ingredients until a soft dough forms; avoid overmixing.

Fold in the mini chocolate chips or chosen mix-ins until evenly distributed in the dough.

Divide the dough in half, shape into logs about 2 inches in diameter, wrap tightly in plastic wrap, and chill for at least 2 hours.

Preheat the oven to 350°F (175°C) and line baking sheets with parchment paper.

Unwrap the logs and roll in colorful sprinkles if desired. Slice into 1/4-inch thick rounds and place on prepared sheets.

Bake for 10-12 minutes until edges are lightly golden and centers remain soft.

Cool on the baking sheets for about 5 minutes before transferring to wire racks to cool completely.