01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a food processor, blend spinach leaves until finely chopped to an almost puree consistency. Set aside.
03 - In a large bowl, cream together softened butter and sugar until light and fluffy.
04 - Beat in egg and vanilla extract until fully combined.
05 - Stir in spinach puree, mixing until well incorporated throughout the wet mixture.
06 - In a separate bowl, whisk together flour, baking powder, and salt.
07 - Gradually add dry ingredients to wet mixture, stirring just until combined. Do not overmix.
08 - If using nuts or chocolate chips, fold them into the dough until evenly distributed.
09 - Drop rounded tablespoons of dough onto prepared baking sheets, spacing approximately 2 inches apart.
10 - Bake for 12 to 15 minutes, or until edges are lightly golden brown.
11 - Allow cookies to cool on baking sheet for 5 minutes, then transfer to a wire rack for complete cooling.