1. Prepare the Crust:

1. In a large bowl, cream together the softened butter and sugar until light and fluffy. Beat in the egg and vanilla extract.
2. In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until a smooth dough forms. Divide dough in half, shape into discs, wrap in plastic, and chill for at least 1 hour.
3. Preheat oven to 375°F (190°C). On a floured surface, roll out one disc of dough to 1/4-inch thickness. Use snowflake-shaped cookie cutters to cut out shapes and place them on a parchment-lined baking sheet.
4. Bake for 7-9 minutes, or until the edges are just beginning to turn golden. Let cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.
5. For the icing, whisk together the powdered sugar and meringue powder. Add the warm water and beat on high speed until stiff, glossy peaks form, about 5-7 minutes. Add a few drops of blue food coloring if desired. Pipe or spread icing onto cooled cookies to create snowflake designs. Let icing set completely before serving.