Preheat oven to 325 degrees. Make topping by combining 1 cup flour with brown sugar, a stick of softened butter and 1 teaspoon cinnamon in a medium 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 bit at a time. Add half n half 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 cake for 50 minutes, or until the edges just begin to turn light brown. Cool and slice into 8 pieces. Serves 8.