Preheat oven to 350°F (175°C). Line an 8×8-inch baking pan with aluminum foil and spray the foil with cooking spray; set the prepared pan aside.

In a large, microwave-safe bowl add ½ cup unsalted butter (1 stick) and microwave until melted, about 1 minute on high. Let the melted butter cool for a minute so it is warm, not hot.

Add 1 large egg, 1 cup light brown sugar (packed), and 1 tablespoon McCormick Pure Vanilla Extract to the cooled melted butter. Whisk until smooth and uniform.

Add 1 cup all-purpose flour and ½ teaspoon salt to the wet mixture. Stir with a spatula or spoon until just combined; do not overmix.

Fold in ½ cup red, white, and blue sprinkles until evenly distributed in the batter.

Turn the batter into the prepared 8×8-inch pan and smooth the top lightly with a spatula.

Bake at 350°F for 20–24 minutes, or until the top is set in the center. A toothpick inserted in the center should come out clean or with a few moist crumbs but no wet batter. Do not overbake; the blondies will firm as they cool.

Remove the pan from the oven and set it on a wire rack. Cool completely in the pan for at least 90 minutes before cutting or frosting.

After cooling, cut the baked slab into star shapes using star-shaped cookie cutters, or cut into pieces of your desired shape. You may also leave the slab whole to frost before cutting.

To make the frosting, place ¼ cup unsalted butter (softened) in a large bowl. Beat with an electric mixer until light and creamy.

Add about 2 to 2 1/4 cups confectioners’ sugar gradually, beating to incorporate and scraping down the bowl as needed. Add 2 to 3 teaspoons cream or milk slowly, stopping when the frosting reaches a spreadable consistency you like.

Add McCormick Red Food Color from the 1-ounce bottle a few drops at a time, stirring after every 10–15 drops, until you reach the desired red color.

Spread the frosting over the cooled stars (or over the whole pan if you left it intact). Add red, white, and blue sprinkles as desired for decorating.

Store any leftover frosting airtight in the refrigerator for up to two weeks.