Preheat and prepare pan. Position a rack in the center of your oven and preheat the oven to 350°F (177°C). Spray a 9”x5” loaf pan with cooking spray, or line with parchment paper and then spray with cooking spray.
Make streusel. In a small bowl, stir together the flour, sugars, and lemon zest. Stir in melted butter until a crumbly mixture forms. Set aside.
Combine dry ingredients. In a mixing bowl, whisk together all-purpose flour, granulated sugar, baking powder and salt. Stir in lemon zest. Set aside.
Combine wet ingredients. In a second mixing bowl, whisk together eggs, milk, vanilla and butter.
Combine wet and dry ingredients. Add the dry ingredients to the wet ingredients and mix together with a spatula or wooden spoon just until just combined. Fold in berries..(I toss them in a tablespoon of flour first so they don’t sink in the batter when baking. Do not overmix.
Assemble. Spoon batter into prepared loaf pan. Sprinkle on streusel.
Bake. Bake in a preheated 350°F (177°C) oven for 50-60 minutes until a toothpick inserted into the middle of bread comes out clean or with a few moist crumbs clinging to it (no wet batter) and top springs back to the touch when lightly touched. Remove from the oven and cool completely in the pan on a wire cooling rack.