In a large bowl, cream together the butter and sugar until light and fluffy.

Add the egg and vanilla extract, and mix until fully combined.

In a separate bowl, whisk together the flour, baking powder, and salt.

Gradually add the dry ingredients into the wet ingredients. Mix until a soft dough forms.

(Optional) Wrap the dough in plastic wrap and chill for 30 minutes for easier handling.

Preheat oven to 350°F (175°C).

Roll out the dough to about ¼ inch thick on a lightly floured surface.

Use a round cookie cutter or shape of choice and place cookies on a parchment-lined baking sheet.

Bake for 8–10 minutes, or until the edges are just barely golden.

Remove from the oven and immediately use a shamrock-shaped cookie cutter to cut out the shamrock shape while cookies are still soft.

Let cool on the pan for 5 minutes, then transfer to a wire rack to cool completely.

Once cookies are completely cooled, ice with green icing.

Decorate with sprinkles or edible glitter as desired.

Let icing set before serving or storing.