1. Preheat your oven to 350 F (175 C). Lightly grease and flour an 8×8 inch square baking pan or a 9-inch round cake pan.

2. In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, brown sugar, baking soda, ground cinnamon, and salt. Make sure there are no lumps and everything is evenly distributed.

3. In a separate medium bowl, whisk together the melted butter, large egg, vanilla extract, and milk. Ensure the egg is well incorporated and the mixture is smooth.

4. Pour the wet ingredients into the dry ingredients. Stir gently with a spoon or spatula until just combined. Be careful not to overmix; a few small lumps are perfectly fine.

5. Fold in the room temperature sourdough discard. Mix until it’s just incorporated into the batter.

6. Pour the batter evenly into your prepared baking pan. In a small bowl, combine the 2 tablespoons of granulated sugar and 1 teaspoon of ground cinnamon for the topping. Sprinkle this mixture evenly over the top of the cake batter.

7. Place the pan in the preheated oven and bake for 25-30 minutes. The cake is done when a wooden skewer or toothpick inserted into the center comes out clean or with only a few moist crumbs attached. The top should be golden brown and the cinnamon sugar topping will be fragrant.

8. Remove the cake from the oven and let it cool in the pan on a wire rack for at least 15-20 minutes before slicing and serving. This allows the cake to set properly and makes for cleaner slices.