In a large bowl whisk the sugar, vanilla and butter until light and creamy.
Whisk together the flour, baking powder and salt in a separate bowl.
Add the flour mixture to the butter and stir until the mixture comes together in a soft dough, gradually adding milk. Transfer the dough onto a working surface.
Divide the dough in half. Using the blue food coloring, tint half blue.
Shape each piece into an even 8-inch log, then cut each log in half lengthwise and press white and blue halves together. Wrap each log with plastic and freeze for 10 minutes or until SLIGHTLY firm.
Preheat your oven to 350° F. Line a large baking sheet with parchment paper. Set aside.