In a large bowl, combine 1-1/2 cups flour, sugar, cinnamon, baking powder and soda, and salt until well mixed. Cut in the butter, using a pastry blender (or pulling 2 knives through ingredients in opposite directions) until mixture is crumbly. Add buttermilk, egg and vanilla. Beat with electric mixer on medium speed for 1 minute. Spread in an 8-inch square pan that has been greased on the bottom only.
In a small bowl, mix all the streusel ingredients, except the chocolate chips, with a fork until mixture is crumbly. Sprinkle over batter and then sprinkle with chocolate chips. Recipe calls for just 1/4 cup chips, but I think 1/2 cup would be better. Use your own judgement, depending on how much chocolate you like.
Bake in a preheated 350-degree oven for 35 to 45 minutes, or until toothpick inserted near center comes out clean. Cool for 30 minutes and serve warm.