To make the streusel topping, whisk together the flour, brown sugar, and salt. Place into a food processor and add the cubes of butter. Pulse until mixture begins to form pea-size crumbles.

In a small bowl stir together the cinnamon and granulated sugar and set aside.

Preheat the oven to 350 degrees. Line a 8x8 glass baking dish with parchment paper, leaving a two inch overhang on each side.

Whisk together the flour, baking soda, cream of tarter, and salt. In a separate bowl, whisk together the butter, both sugars, and eggs. Add the flour mixture and stir until combined.

Spread half the batter on the bottom of your baking dish using a spatula. Sprinkle half the cinnamon and sugar mixture over the batter evenly. Dollop the remaining batter on top and spread evening. Top with the streusel topping and sprinkle the rest of the cinnamon and sugar over the streusel topping.

Bake for 30-35 minutes or until a toothpick inserted into the center comes out clean.

Let the coffee cake cool completely and then slice and serve. Store in an air-tight container at room temperature for up to 3-4 days.