
This is an adapted recipe from my dad's old Maida Heatter which is now out of print. It's not the easiest recipe, but it's so worth the work. And definitely use fresh lemon zest. It makes all the difference.
Preheat the oven to 375℉. Butter a 9" square baking dish (with at least 2" high sides) and dust with flour.
in a small bowl, combine the flour, sugar, cinnamon, and salt. Cut in the butter with a pastry blender or 2 knives until the topping is crumbly. Set aside.
In a bowl, sift together the flour, baking powder, and salt. Stir to mix well. In a larger bowl and using a hand mixer, beat together the butter, sugar, and lemon zest until the batter is light and frothy. Beat in the egg and vanilla. Then add in half of the milk, then a third of the dry ingredients, repeating until you use up all the milk mixture and dry ingredients. Make sure to end with the dry ingredients. The battle will be very stiff--it's supposed to be. Fold in the blueberries until they are distributed evenly throughout the dough.
Turn the dough into the pan and smooth out until it is even across the pan. If using the pecans, sprinkle them on top of the dough. Then cover the dough with the crumb topping.
Bake for 40 minutes or until a toothpick stuck in the center comes out clean. Cool the cake on a baking rack. Once cool, dust with confectioners' sugar and serve.