In a large bowl, whisk together the remaining 7 tablespoons of butter, granulated sugar, egg, salt, cinnamon, and vanilla until smooth (approximately 1 minute). Switch to a flexible spatula, stir in baking soda, and gently add flour. Stir until well combined. Place the bowl in the fridge until the dough is less sticky but still soft and pliable (about 15-20 minutes).