Follow these step-by-step instructions to create perfect individual crumble cups every time. The process is straightforward and forgiving, making it an excellent recipe for bakers of all skill levels.

1. Preheat Oven and Prepare Pan: Begin by preheating your oven to 375°F (190°C). This ensures the crumble cups start baking immediately and cook evenly. Prepare a standard 12-cup muffin tin by lining it with paper or silicone liners. If you don’t have liners, you can grease and flour the tin very well, but liners make for the easiest removal and cleanup. Place the prepared muffin tin on a larger baking sheet. This is a pro-tip to catch any potential bubbling or spills, keeping your oven clean.
2. Make the Blueberry Filling: In a medium-sized mixing bowl, combine the blueberries (fresh or frozen), granulated sugar, all-purpose flour (or cornstarch), fresh lemon juice, and vanilla extract. Gently stir everything together until the blueberries are evenly coated. The flour/cornstarch might look a little chalky at first, but it will dissolve as it bakes. Set this bowl aside while you prepare the topping. This allows the berries to macerate slightly, drawing out their juices.
3. Create the Crumble Topping: In a separate, larger mixing bowl, whisk together the dry ingredients for the topping: the old-fashioned rolled oats, all-purpose flour, packed brown sugar, ground cinnamon, and salt. Whisking ensures that the cinnamon and salt are evenly distributed throughout the mixture.
4. Cut in the Cold Butter: Add the small cubes of cold butter to the dry topping ingredients. Using a pastry blender, two knives, or your fingertips, cut the butter into the flour and oat mixture. Continue working the butter in until the mixture resembles coarse crumbs with some pea-sized pieces of butter still visible. The key is to work quickly so the butter doesn’t melt from the heat of your hands. Do not overmix; you want visible pockets of butter to create that perfect crispy texture.
5. Assemble the Crumble Cups: Now it’s time to build your mini desserts. Spoon the blueberry filling evenly among the 12 prepared muffin cups. Each cup should be about two-thirds full. Don’t be tempted to overfill them, as the filling will bubble up significantly during baking.
6. Add the Topping: Generously sprinkle the crumble topping over the blueberry filling in each cup. Press down gently on the topping to help it adhere slightly. You should use all of the topping; a thick layer is what makes these so irresistible. The topping will seem plentiful, but it’s the perfect ratio for a crunchy lid on each cup.
7. Bake to Golden Perfection: Place the baking sheet with the muffin tin into the preheated oven. Bake for 25-30 minutes. You’ll know they are done when the crumble topping is a deep golden brown and you can see the blueberry filling bubbling up around the edges. The aroma will be incredible!
8. Cool Before Serving: This is a very important step! Remove the baking sheet from the oven and place it on a wire rack. Let the crumble cups cool in the muffin tin for at least 15-20 minutes. This allows the molten filling to set up, making the cups stable enough to be removed from the tin without falling apart. After this initial cooling period, you can carefully lift them out and let them cool further on the wire rack or serve them warm.