In a large bowl, cream together the softened butter and granulated sugar using a mixer until light and fluffy (about 2-3 minutes).

Add the egg and vanilla extract, beating until well combined. Slowly add the green food coloring until the dough reaches your preferred shade of green.

In a separate medium bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Do not overmix.

Form the dough into a disc, wrap tightly in plastic wrap, and refrigerate for 30 to 45 minutes.

Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

Remove dough from the fridge. For each turtle, roll one 1-inch ball for the shell, one slightly smaller ball for the head, and four small balls for the legs/flippers.

Place the large shell ball on the baking sheet. Gently press the head and four legs around the base of the shell to attach them.

Use a standard fork to press down gently on the shell ball, flattening it slightly. Press again in the opposite direction to create a crosshatch pattern.

Use an edible marker, a dot of black icing on a toothpick, or tiny sprinkles to carefully add two eyes to the turtle's head.

Bake for 8-10 minutes, or until the cookies are just set and the edges of the legs are barely starting to turn golden brown. Let cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.