In a large bowl, cream the butter and sugar with an electric mixer until light and fluffy. Add the eggs and vanilla, and beat until smooth.

In a medium bowl, combine the flour, baking powder, and salt with a whisk. Add to the butter mixture, beating just until combined.

Scrape half of the dough onto a large sheet of plastic wrap. Flatten into a disk, wrap, and place in the refrigerator to chill for 1 hour or use within 3 days. Repeat with the other half of the dough. If freezing, also wrap in aluminum foil and place in the freezer for up to one month.

Preheat oven to 375 degrees. Working with one disk of dough at a time, roll out on a lightly floured surface to 1/4" thickness for thick, soft sugar cookies, or 1/8" for thinner, crispier cookies.

Cut into desired shapes using lightly floured cookie cutters. Place cookies on a parchment lined baking sheet about 1 1/2" apart. Sprinkle with sanding sugar, or leave plain and ice after they’re baked.

Bake for 6-8 minutes or until lightly browned on the edges. Be careful not to over bake — the cookies are done as soon as the tops feel dry. Cool completely on a wire rack.

For the Vanilla Icing, sift the powdered sugar into a medium bowl. Stir in 2 tablespoons of hot water, corn syrup, and vanilla until continue to stir until smooth. Add more hot water one tablespoon at a time if necessary.

Spread the icing over the tops of the cooled cookies, or pipe it with a pastry bag fitted with a fine tip. Immediately sprinkle with sanding sugars, and decorate with the candies of your choice.

Let the cookies stand at room temperature until the icing has set, about 30 minutes to 1 hour.