Preheat oven to 350 degrees. In a large bowl, cream butter and sugar. Add one egg at a time, beating well after each addition. Add vanilla and beat to incorporate. Measure and blend all dry ingredients in a separate bowl and set aside. Add abou 1/3 milk and 1/3 zucchini to egg mixture and blend well. Add about 1/3 of the dry ingredients and blend well. Repeat two more times until all ingredients are blended. Prepare 2 loaf pans with vegetable oil spray and divide batter equally between the pans. The pans should be about 2/3's full. Place pans in oven on the middle rack and bake about 1 hour. Text for doneness with a long toothpick or wooden skewer. I use glass pans, so a dark non-stick pan would cook in less time.