Preheat your oven to 350°F and butter an 8x8 baking dish.

In the prepared dish, toss the sliced apples with 1 tablespoon flour, 2 tablespoons brown sugar, 1/2 teaspoon cinnamon, and a pinch of salt until well combined.

For the topping, mix together 1 tablespoon brown sugar, 1 tablespoon flour, and a generous sprinkle of cinnamon. Cut in the cold butter using a fork or your fingers until the mixture is crumbly. Stir in the chopped walnuts.

Sprinkle the topping evenly over the apples.

Bake for 35-40 minutes, until the apples are tender and bubbling. Let cool for about 10 minutes before serving. Enjoy warm, optionally with vanilla ice cream!