In a large mixing bowl, cream together the butter and sugar until light and fluffy, about 3-4 minutes. Add in the egg and vanilla extract, mixing well. Gradually add the flour, baking powder, and salt until just incorporated into a soft dough.

Wrap the dough in plastic wrap and refrigerate for at least 30 minutes.

On a floured surface, roll out the chilled dough to about ¼ inch thick. Use a heart-shaped cookie cutter to cut out the cookies and place them on lined baking sheets.

Bake in a preheated oven at 350°F (175°C) for 10-12 minutes, or until edges are golden. Let cool for 5 minutes on the baking sheet before transferring to a wire rack.

Mix powdered sugar with a splash of water or lemon juice to create icing. Decorate cookies with icing and sprinkles once completely cool.

Arrange the decorated cookies on a platter or package them in boxes for gifting.