Preheat oven to 325 degrees F. Make topping by combining 1 cup flour with brown sugar, 1/2 cup softened butter, and 1 teaspoon cinnamon in a bowl. Mixture should have the consistency of moist sand. Add 1/2 cup chopped pecans. In a large bowl, cream together 1 cup butter, 3/4 cup light brown sugar and 1/2 cup granulated sugar with an electric mixer until smooth and fluffy. Add eggs and vanilla and mix well. In a separate bowl combine flour, baking powder and salt. Add this dry mixture to the moist ingredients a little at a time. Add milk and mix well. Spoon the batter into a 9 x 13-inch baking pan that has been buttered and dusted with a light coating of flour. Sprinkle the crumb topping over the batter. Be sure the topping completely covers the batter. Bake 50 minutes or till the edges just begin to brown. Cool.