Preheat oven to 350 degrees. Lightly grease a 9x9-inch baking dish and set aside. In a large mixing bowl, combine flour and sugars; cut in butter until crumbly. Remove 1/2 cup of flour mixture and set aside for topping. Add baking soda, egg, vanilla extract, and buttermilk to the remaining flour mixture in a large bowl, and blend well. Pour batter into the prepared baking dish. To the reserved flour mixture, add the English Toffee bits, chopped pecans, and mini chocolate chips. Sprinkle evenly over top of batter. Bake for 45 minutes, or until a toothpick inserted into the center comes out clean. Serve warm or at room temperature.