Preheat oven to 350ºF (160ºC). Line an 8.5” x 4.5” (1.5 L) loaf pan with parchment paper.
Streusel Topping: In bowl, combine granulated and brown sugars and flour. Cut in butter until mixture is very crumbly; set aside.
Using electric mixer, cream butter and sugar together. Add eggs, one at a time, beating well after each addition, then vanilla. Combine flour, baking powder, salt and lemon rind. Using wooden spoon, alternately stir dry ingredients and milk into butter mixture, making three additions of dry and two of milk. Gently fold in blueberries. Transfer to prepared pan. Sprinkle with streusel.
Bake in centre of preheated oven for 70 to 75 minutes or until topping is golden and cake tester inserted in centre comes out clean.
If using frozen blueberries, do not thaw. Toss gently with 1 tbsp (15 mL) all purpose flour before folding into batter, to prevent the blueberries from “bleeding”.
The streusel doubles and triples well. Use on top of muffins, open-faced pies and other quick breads.