Combine flour, salt & baking powder in a bowl, mix and set aside.
In another large mixer bowl, cream together the softened butter & sugar.
Once smooth, add the eggs & vanilla and beat well.
Add the flour mixture to the butter mixture a little at a time. Mix until the dough is smooth and flour is fully incorporated.
Remove ½ of the dough & wrap it in plastic wrap - refrigerate at least 1 hour.
With the remaining dough in the bowl- add several drops of food color & beat well until combined & dough becomes the desired color- you can keep adding drops & then beat until you get it to where you want.
Remove the tinted dough & wrap it with plastic wrap. Chill in the refrigerator for 1 hour.
Preheat the oven to 350 degrees.
On a lightly floured surface, roll out each ball of dough separately to about ¼ inch thickness.
Using a pastry brush, apply a little water to the darker layer of the dough.
Roll the lighter color of the dough around the rolling pin and transfer it to the top of the darker colored layer of the dough. A little bit of water will help them stick together.
Trim the edges so you end up with a neat and tidy rectangle.
Gently roll the dough from one of the wider ends to form a log.
Work the log and even it out if the middle is thicker than the ends.
Pour some sprinkles into your hand & brush the outside of the dough with a bit more water and then press the sprinkles into the outside of the dough log.
Wrap the dough in plastic wrap and refrigerate for another hour.
Once chilled, slice the dough into rounds - they should be about ¼" thick. The thinner the blade used to slice them, the better. A thick blade will tend to squish the dough.
Bake in the center of a preheated oven at 350 degrees for approximately 8-10 minutes