Combine the melted butter with the zucchini, egg, kefir, and vanilla and mix well.
1 egg, 1 cup kefir or yogurt *see note if using yogurt, 1 teaspoon vanilla
Add the wet ingredients to the dry ingredients and stir to combine, but don't over mix. The batter will be very thick.
Gently fold in the blueberries. *see note below
1 cup blueberries
Put in prepared loaf pan and cook for 50-60 minutes, until the top is browned and a knife inserted in the middle comes out clean.
Notes
You can substitute yogurt for the kefir. If the yogurt is thick, like Greek yogurt, add a few tablespoons of milk to thin it out.
Blueberries tend to sink to the bottom of baked goods, especially frozen blueberries. You can coat the blueberries with 1 Tablespoon of flour before folding them in to help with the sinking. I usually only do this if I am using frozen blueberries.