In a large bowl, using a hand mixer, cream together the butter and both sugars until fluffy.
½ cup unsalted butter, ¾ cup brown sugar, ¼ cup granulated sugar
Beat in the egg and vanilla.
1 large egg, 1 teaspoon pure vanilla extract
Add in the flour, baking powder, and salt. Mix until just combined. The dough will be very crumbly.
2 cups all-purpose flour, ½ teaspoon baking powder, ½ teaspoon kosher salt
Stir in the white chocolate chips.
½ cup white chocolate chips
Divide the dough into 3 equal portions, add one color to each portion, and mix until the color is uniform.
Food coloring
Take a bit of each of the 3 different colored doughs and roll them together to form a ball. The colors should swirl a bit together. Repeat until you have 6 large cookies
Roll the top and sides of the cookies in your Halloween sprinkles, place on a greased cookie sheet, and refrigerate for at least 30 minutes.
Halloween sprinkles
While the cookies chill, preheat oven to 375°F.
Bake the cookies for 18 minutes.
When the cookies come out of the oven, if there are any spots that look bare, go ahead and add some sprinkles to the hot cookie.
Cool 5 minutes and then transfer to a rack.