Preheat the oven to 450 degrees and line a baking sheet with parchment paper.
In a mixing bowl, add the 2 1/4 cup Bisquick and stir in the 1/2 tsp of cinnamon. Next, add the 4 tbsp of cold salted butter and cut it into the Bisquick until it resembles pea-size crumbs. After this, add the egg and stir it in. Finally, add 2/3 cup of buttermilk and mix until no dry ingredients remain.
Scoop out 8 equal scoops of the shortcake dough onto the baking sheet. Make sure to leave room between them so they don't stick together while baking.
Place the baking sheet in the oven on the middle rack and bake for 9-12 minutes, or until the tops of the shortcakes are just turning golden brown. Once they are finished baking, remove them from the oven and let them cool on the baking sheet.