In a medium bowl, cream softened butter and maple syrup until light and fluffy (use a hand mixer, immersion blender or beat vigorously with a fork).
Beat in the egg yolk, vanilla, lemon zest, lemon juice, and chopped basil until fully combined.
In a separate bowl, whisk together flour, baking powder, and salt. Gradually add to wet ingredients and mix just until a dough forms. Do not overmix!
Shape into a flat disc, wrap in parchment paper or plastic wrap, and refrigerate for at least one hour.
Preheat oven to 350F. Remove dough from the fridge and let it soften slightly. Roll between two sheets of parchment paper to about ¼ inch thick. Cut into desired shapes and roll in brown sugar.
Place cutouts (on parchment paper) onto a baking sheet. Bake for 8-10 minutes, until the edges are just turning golden. Let cool a few minutes before transferring to a wire rack.
While the cookies are baking, create glaze by whisking powdered sugar with lemon juice until smooth. Stir in chopped basil and maple syrup if using. Once your cookies have cooled completely, drizzle the glaze over them with a spoon or a piping bag for a delicate pattern then immediately sprinkle crushed pistachios over the wet glaze so they stick. Let set for a couple minutes then enjoy!