Step 1: Prepare the Dough

• The butter and sugar should be melted. Use a hand or stand mixer to beat them together in a medium bowl on medium speed for about 2 minutes, or until the mixture is light and fluffy. If you need to, scrape the bowl clean.
• Mix in the egg yolk and vanilla extract until fully combined.
• In a separate bowl, whisk together the flour, baking powder, and salt.
• Gradually add the dry ingredients to the wet mixture, mixing just until combined.
• Shape the dough into a disc, wrap it in plastic wrap, and refrigerate for at least 30 minutes to firm up.

Step 2: Roll and Cut

• Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.
• On a lightly floured surface, roll out the chilled dough to about ¼ inch thick.
• Use a heart-shaped cookie cutter to cut out 12 cookies.

Step 3: Bake

• Place the cookies on the prepared baking sheet about 1 inch apart.
• Bake for 10-12 minutes, or until the edges just start to turn golden.
• Let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

Step 4: Make the Glaze

• In a small bowl, whisk together the powdered sugar, milk, and vanilla extract until smooth.
• If the glaze is too thick, add a tiny bit more milk; if too thin, add more powdered sugar.
• Divide into bowls and tint with gel food coloring if desired.

Step 5: Decorate

• Use a spoon or piping bag to apply the glaze to the cooled cookies.
• Spread with the back of a spoon or leave it smooth for a shiny finish.
• Decorate with sprinkles or edible glitter before the glaze sets.

Let cookies sit for 30 minutes until the glaze hardens before serving or storing.