Soften butter at room temperature. Preheat oven to 180 C (350 F). Mix brown sugar, butter, egg, and lemon zest together. Stir in flour, baking soda, cream of tartar, salt, and ginger. Shape dough into 2.5 cm balls. Top with granulated sugar. Cook on a parchment paper lined cookie sheet for 10 to 11 minutes, or when only a light indentation can be made with a knife.