These lemon thumbprints are a lemon lovers’ dream cookie! Enjoy sweet, soft lemon sugar cookie filled with lemon curd and drizzled with lemon icing. I like to make the lemon curd from scratch because the flavor is superior (honestly, it’s just so good!), but feel free to use store-bought. Instead of lemon curd, you can substitute raspberry, strawberry, or apricot preserves/jam.