Step 1: Preheat your oven to 375°F (190°C). Lightly grease a small ramekin (about 6-8 oz) or oven-safe dish.
Step 2: Prepare the apples: In the prepared ramekin, combine the diced apple, 1/2 tbsp granulated sugar, 1/4 tsp ground cinnamon, and optional lemon juice. Stir gently to coat.
Step 3: Make the browned butter: In a small, light-colored saucepan, melt 1 tbsp unsalted butter over medium heat. Continue to cook, stirring occasionally, until the butter turns a rich golden brown and nutty aroma, with tiny brown flecks appearing at the bottom. This should take 3-5 minutes. Immediately pour the browned butter into a separate small bowl to stop it from burning.
Step 4: Divide the browned butter: Pour about 1/2 teaspoon of the browned butter over the apples and stir gently. This infuses the apple mixture with that signature nutty flavor, creating a delicious base for your single-serve apple crisp.
Step 5: Prepare the crisp topping: To the remaining browned butter in the bowl, add the rolled oats, all-purpose flour, brown sugar, pinch of salt, and pinch of cinnamon. Mix with a fork or your fingertips until well combined and crumbly.
Step 6: Assemble and bake: Sprinkle the oat topping evenly over the apples in the ramekin. Place the ramekin on a small baking sheet (to catch any potential spills) and bake for 20-25 minutes, or until the topping is golden brown and the apples are tender and bubbling. The aroma of this single-serve apple crisp will fill your kitchen!
Step 7: Serve: Carefully remove the single-serve apple crisp from the oven. Let it cool for a few minutes before serving. Enjoy warm, perhaps with a scoop of vanilla ice cream or a dollop of whipped cream, for the ultimate single-serve apple crisp experience.