blueberry crumb cake

Name: blueberry crumb cake
Cuisine: American
Ingredients: 5 tablespoons (40 grams) all-purpose flour; 1/2 cup (100 grams) granulated sugar; 1 teaspoon ground cinnamon; 4 tablespoons (1/4 cup, 2 ounces or 55 grams) unsalted butter, cold is fine; Pinch of salt; 2 cups minus 1 tablespoon (i.e. 1 3/4 cups + 3 tablespoons or 240 grams) all-purpose flour; 2 teaspoons baking powder; 1/2 teaspoon table salt; 4 tablespoons (1/4 cup, 2 ounces or 55 grams) unsalted butter, softened; 3/4 cup (150 grams) granulated sugar; Zest of 1 lemon; 1 large egg; 1 teaspoon vanilla extract; 1 pint (2 to 2 2/3 cups, 12 to 16 ounces, or 340 to 455 grams; see Note) fresh blueberries, clean and dry; 1/2 cup milk, whole is ideal, any kind should work; 1/2 cup (55 grams) walnuts, chopped medium fine (optional); Confectioners’ sugar, for dusting (optional)