Preheat oven to 350℉. Prepare baking pan with butter and set aside.
In a large bowl, beat the eggs, butter, vanilla, and sugar until creamed. Fold in zucchini. Mix dry ingredients and slowly stir into batter. Fold in blueberries.
Bake 35-40 minutes, or until toothpick placed in the center comes out clean. Cool completely before frosting.
Frosting
Combine all ingredients in a large bowl and whisk (electric whisk or kitchenaid recommended) until creamy.
Notes
If baking as a loaf, bake at 350F for 45-50 minutes.
Instead of frosting, I suggest topping a loaf with the lemon glaze from my Blueberry Lemon Scones