Heat oven to 350°F (325ºF for dark or nonstick pan). Grease bottom only of 8-inch square pan with shortening or spray bottom with cooking spray.
In large bowl, stir 1 1/2 cups flour, the granulated sugar, cinnamon, baking powder, baking soda and salt until mixed. Cut in butter, using pastry blender (or pulling 2 table knives through ingredients in opposite directions), until mixture is crumbly. Add buttermilk, egg and vanilla. Beat with electric mixer on medium speed 1 minute. Spread in pan.
In small bowl, mix all streusel ingredients except chocolate chips with fork until mixture is crumbly. Sprinkle over batter. Sprinkle with chocolate chips.
Bake 35 to 45 minutes or until toothpick inserted in center comes out clean. Cool 30 minutes. Serve warm.