Beat the softened butter and granulated sugar for 2–3 minutes until creamy.
Add the egg and vanilla extract and mix until combined.
In a separate bowl, whisk together the flour, baking powder, and salt.
Gradually add the dry ingredients to the butter mixture and mix just until a soft dough forms.
Divide the dough into two discs, wrap, and refrigerate for 1 hour.
Preheat the oven to 350°F (175°C) and line baking sheets with parchment paper.
Roll the chilled dough on a lightly floured surface to approximately 1/4-inch thickness.
Cut into apple shapes and transfer carefully to the prepared baking sheets.
Bake for 9–11 minutes until set with only lightly golden edges.
Cool for 5 minutes on the baking sheet, then transfer to a cooling rack.
Cool completely before decorating.
Whisk together powdered sugar, 4 tablespoons milk, corn syrup, and vanilla to make the icing. Add additional milk gradually if necessary.
Divide the icing and color the largest portion red, with smaller portions green and brown.
Decorate each cookie with a red apple body, small green leaf, and brown stem.
Allow the icing to set completely before storing or packing.