Bring butter, eggs, and sour cream to room temperature.

Shred the zucchini and roll in clean tea towel to remove excess moisture. If zucchini is still overly wet (i.e., the tea towel is soaked), re-roll and blot the zucchini again in a clean, dry tea towel.

Sieve dry ingredients together into bowl. Set aside.

With stand mixer fitted with paddle attachment, beat the butter at medium speed until soft. Blend in the sugars and beat well. Add the whole egg and beat then follow with the addition of the egg yolk, beating until well blended. Beat in the sour cream, maple syrup, and vanilla until combined.

Reduce mixer speed to medium-low and mix in the blotted-dry shredded zucchini. With mixer on low speed, gradually add the dry ingredients, mixing just until they are combined with the batter.

Remove bowl from mixer stand and stir in the chocolate chips. Cover bowl with plastic wrap and refrigerate for at least 1½ - 2 hours.

Preheat oven to 375°. Line cookies sheets with parchment paper.

Remove cookie dough from the refrigerator. The dough should be firm to the touch. If it is particularly firm, let dough stand at room temperature for 5-10 minutes. Drop dough by tablespoonful onto prepared baking sheet, spacing cookies about 2” apart. Bake for approximately 13-14 minutes, rotating baking sheets partway through the baking. Let cookies rest on cookie sheets for 4-5 minutes after removing from oven and before transferring to a wire rack to cool completely.