Prep the apples: Peel (optional), core, and dice the apples into small 1/2-inch pieces. Smaller pieces cook faster and get tender without turning mushy.

Start the filling: In a skillet over medium heat, melt 1 tablespoon butter. Add apples, brown sugar, 1 tablespoon granulated sugar, 1 1/2 teaspoons cinnamon, nutmeg, lemon juice, and a pinch of salt. Cook 5–7 minutes, stirring, until the apples soften and release juices.

Thicken it: Sprinkle in cornstarch and stir well. Cook 1–2 minutes until the juices turn glossy and slightly thick. Remove from heat and stir in vanilla. Taste and add the remaining sugar if you want it sweeter.

Make the crunchy layer: In a small pan, melt remaining 2 tablespoons butter. Toss with oats, crushed graham crackers, nuts (if using), and 1/2 teaspoon cinnamon. Toast over low heat for 2–3 minutes until lightly golden and fragrant.

Assemble the cups: Spoon a thin layer of the crunchy mix into the bottom of 6 small glasses, ramekins, or jars. Add warm apple filling, then finish with another layer of the crunchy mix on top.

Serve: Enjoy warm as is, or top with whipped cream or a small scoop of vanilla ice cream. For cleaner layers, let cups sit 5 minutes to set slightly.