Preheat oven to 350°F; line baking sheets with parchment paper.
Beat butter and sugar until fluffy. Add egg, lemon juice, zest, and vanilla; mix well.
Whisk flour, baking powder, baking soda, and salt; add to wet mixture and mix until combined.
Scoop 1 tbsp dough per cookie; roll into balls and flatten slightly on baking sheets.
Bake for 10-12 minutes until edges are set. Cool on sheets for 5 minutes; transfer to a rack.
Mix powdered sugar, lemon juice, and zest for glaze; drizzle over cooled cookies.
Garnish with lemon zest, white chocolate drizzle, and lavender. Serve at room temperature.