Sift powdered sugar into a medium bowl. Add 6 teaspoons milk, corn syrup, and extract. Stir vigorously until icing is smooth.
If needed, add additional milk to thin icing more. You've reached the correct consistency for frosting if a scoop of icing slowly falls off the spoon. If making colored icing, divide into bowls and add food coloring.
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Notes
TIPS FOR MAKING SUGAR COOKING ICING AND DECORATING
Start with a couple teaspoons less of milk. Add the last 2 teaspoons as necessary.
To achieve the perfect consistency add more powdered sugar to thicken and a touch of milk to thin.
You've reached the correct consistency for frosting if a scoop of icing slowly falls off the spoon.
Traditionally sugar cookie icing is flavored with almond or vanilla extract, but orange, lemon, maple, or coconut extracts can also be substituted.
Sifting the powder sugar before adding milk will eliminate any potential lumps in the frosting.
Sugar cookie icing can be piped as an outline and filled in for pristine edges. Alternatively, it can also be spread with a small knife and decorated with sprinkles.
This frosting hardens quickly so have sprinkles ready to put on immediately.
Before stacking or wrapping cookies, make sure the icing is completely hard. Set cookies on a baking sheet for 12 hours.