Preheat the oven to 350 degrees F and line a baking sheet with parchment paper.
In a mixing bowl, beat the softened butter and sugar until light and fluffy.
Add the egg, lemon zest, and lemon juice to the bowl and mix until combined.
In a separate bowl, whisk together the flour, baking powder, and salt.
Gradually stir the dry ingredients into the wet mixture until a soft dough forms.
Scoop the dough into 4 equal portions and place them on the baking sheet, spacing them apart.
Bake for 10 to 12 minutes until the edges turn lightly golden.
Remove the cookies from the oven and immediately press 3 candy corn pieces onto each warm cookie.
Let the cookies cool on the baking sheet for 5 minutes before moving them to a wire rack.