01 - Preheat oven to 350°F. Line a baking sheet with parchment paper.
02 - Wash, dry, and finely chop the kale leaves. Set aside.
03 - In a medium bowl, whisk together flour, baking soda, baking powder, and salt.
04 - In a large mixing bowl, cream butter with both sugars until light and fluffy, about 2-3 minutes.
05 - Beat in the egg and vanilla extract until combined.
06 - Gradually add the dry ingredients to the wet mixture, mixing just until incorporated.
07 - Fold in chopped kale and any optional mix-ins.
08 - Scoop tablespoon-sized balls of dough onto the prepared baking sheet, spacing 2 inches apart.
09 - Bake for 11-13 minutes, until edges are golden but centers are still soft.
10 - Let cool on the sheet for 5 minutes, then transfer to a wire rack to cool completely.