In a small mixing bowl, whisk together flour, baking powder, and salt; set aside.
In a large mixing bowl, using a handheld electric mixer on medium speed, cream together butter and sugar until light and fluffy. about 2 minutes. Beat in eggs 1 at a time. Stir in vanilla.
Gradually add the flour mixture to butter mixture and beat just until combined. Shape dough into a disk and wrap tightly with plastic wrap. Refrigerate a minimum of 1 hour up to overnight.
Preheat oven to 400 degrees.
Roll dough out on a floured surface to 1/4 inch thick. Use cookie cutters to cut into desired shapes. Place cookies on ungreased cookie sheets 1 inch apart and bake in preheated oven 6-8 minutes. Cool 5 minutes on baking sheets then remove to a wire rack and cool completely.
Icing:
In a mixing bowl, stir together confectioners’ sugar, corn syrup, and 2 tablespoons of milk until smooth. Add more milk, a little at a time to thin icing to a pourable consistency. If desired, divide icing into smaller bowls and tint with food coloring.
Decorating:
Set completely cooled cookies on a wire rack set over a rimmed baking sheet. Slowly spoon/poor icing over cookies. Decorate with colored sugar, jimmies, sprinkles. Let icing set completely before serving or storing.