Preheat & Prep. To start, preheat oven temperature to 350 degrees F. Line a light colored metal muffin pan with 12 parchment paper liners. Start boiling a pan of water to use for the modified hot water bath later.
Mix Crust. In a medium bowl, combine gluten-free graham cracker crumbs, melted butter, and 2 Tablespoons granulated sugar. Stir until evenly blended.
Divide & Pat Out Crust. Add a heaping tablespoon of the crust mixture to each parchment paper cup and use the back of the tablespoon (or clean fingers) to gently pat down the crust. It doesn't need to be super compacted, but should look even and sealed around the edges.
Pre-Bake Crust & Cool. Bake crust for 8 minutes and set the pan aside to cool slightly while you mix up the filling.
Mix Cream Cheese & Sugar. In the bowl of a stand mixer (or a large mixing bowl), beat softened cream cheese and granulated sugar on medium-low speed with the paddle attachment (or a hand mixer) 2-3 minutes, or until evenly blended and creamy.
Finish The Filling. Scrape down the sides of the bowl and add sour cream, vanilla, lemon zest, and cornstarch. Mix on LOW speed just until blended, then add eggs 1 at a time on LOW speed until just mixed. (Try not to over-mix here, since incorporating extra air can cause the cheesecakes to sink later.)
Add Filling To Crust. Spoon or pour cheesecake batter over the graham cracker crusts (it's ok if the crust is still slightly warm!). Gently shake the pan or gently tap on the counter to remove any air bubbles.
Make Hot Water Bath & Bake. Pour boiling water into a 9x13 metal or ceramic pan (I like to place mine on a cookie sheet for stability) and place on the rack underneath the center. Add muffin pan with the cheesecakes to the center rack above the water bath and bake 25-28 minutes or until just set. (A small wobble in the center is fine!) The cheesecakes will look slightly puffed at this point.
Cool, Then Chill. Remove the muffin pan from the oven and let the cheesecakes cool at room temperature 45 minutes. Transfer pan to the fridge and chill uncovered at least 4 hours or until completely cold. Cheesecakes will settle as they chill, and will have a slight indent in the center, but shouldn't look sunken!
Serve & Store. Remove cheesecakes from the pan (I leave them wrapped in parchment paper wrapper for easy serving) and enjoy with your favorite toppings. Store leftover cheesecakes covered in the fridge 3-4 days or freeze without toppings in a single layer up to 2 months. For best results, store the cheesecakes without toppings.