Preheat oven to 375 degrees F. Grease or line with paper cups either a regular or "Texas" muffin pan. Regular makes about 18 muffins, "Texas" makes about 9. I made "Texas" size.
For crumb topping: in a small bowl, mix all ingredients except the melted butter. While stirring, add the butter until you get clumps about the size of small peas. You may have to add a tablespoon or 2 MORE flour to get good crumbs. This is weather dependent. Set aside.
For the muffins: In a medium bowl, stir the 1 cup flour, baking powder and salt together. Set aside.
In a large bowl, combine the sugar, eggs, oil, milk, extract and lemon zest. Beat with electric mixer until foamy.
Add the flour mixture to the liquid mixture and beat with electric mixer until well blended and there are no lumps.
In a small bowl, mix frozen berries with the 1 tbs flour (this stops them sinking). Stir berries into muffin batter.
Spoon into prepared pans. I use an old-fashioned ice cream scoop for this. Fill the cups 3/4 full. Top with crumbs.
Bake at 375 degrees F for 30-35 minutes for "Texas" muffins. Regular muffins bake about 20-25 minutes, or until a toothpick inserted in the center comes out clean.
Makes about 18 regular, 9 large.