Preheat your oven to 350°F. Grease an 8x8-inch baking dish and set it aside.
Peel, shred, and squeeze out excess moisture from your zucchini using paper towels.
In a skillet over medium heat, melt 1 tsp butter. Add shredded zucchini, 1/2 tsp cinnamon, and 1/2 tsp apple extract. Sauté for 3–5 minutes until soft. Let cool slightly.
In a large bowl, cream together the butter and erythritol until fluffy.
Add in eggs, vanilla, apple extract, and sour cream. Mix until smooth.
In another bowl, whisk together almond flour, coconut flour, baking powder, cinnamon, and salt.
Stir the dry mixture into the wet mixture, then gently fold in the sautéed zucchini.
Pour the batter into the prepared pan and smooth out the top.
Bake for 33–36 minutes or until a toothpick inserted comes out clean.
Cool completely before slicing into squares. Try not to eat half the pan in one sitting (no judgment if you do).