Preheat your oven to 350°F (175°C).
Use a mortar and pestle or spice grinder to lightly crush the culinary lavender. You can also use a rolling pin and crush the lavender buds in a plastic bag. You want the pieces small enough to blend into the dough but not powdered.
In a medium bowl, whisk together the flour, matcha powder, baking powder, baking soda, and salt.
In a large bowl, beat the softened butter, granulated sugar, and brown sugar until light and fluffy—about 2–3 minutes.
Mix in the egg, vanilla, and ground lavender until combined.
Stir the dry ingredients into the wet mixture until a soft dough forms. If you’re adding white chocolate chips or pistachios, fold them in now.
Scoop tablespoon-sized balls of dough onto a parchment-lined baking sheet, leaving about 2 inches between each. Bake for 9–11 minutes, just until the edges are set and the centers look slightly underbaked.
Let cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.