Preheat the oven to 350ºF (180ºC) and line an 8-inch (20-cm) square baking dish with parchment paper. Set aside.
Make The Apple Filling
In a large bowl, stir together the chopped apples and lemon juice. Add the brown sugar, rye flour, white sugar, cinnamon, and salt and continue to stir the apples until everything is well combined. Set aside.
Make The Rye Crust / Crumble Topping
Add the rye flour, brown sugar, and salt for the crust/topping to another bowl. You can whisk these ingredients together, however, I use my hands to mix in order to break up any larger clumps of brown sugar.
Pour the melted butter into the bowl of dry ingredients. Stir everything together with a fork or rubber spatula to start. To finish, set down the fork and rub the rye flour and butter together between your fingers and thumbs to fully combine.
Assemble The Bars
Scoop out approximately 1 cup (120 g) of rye flour crumble from the bowl and set it aside. Dump the rest of the rye flour mixture into the prepared baking dish. Use your fingers to spread the flour evenly across the bottom of the dish, then use your hands to press and compact the layer down as the bottom crust.
Top the crust with the Red Prince apple mixture. Use a rubber spatula or fork to spread out the apple layer evenly.
Scatter the remaining 1 cup of rye flour mixture that was set aside over the top of the apples. Place the baking dish in the preheated oven and bake the apple crumble bars for 55 to 60 minutes, or until the topping is golden and the fruit is bubbling. Cool completely before slicing and serving.
Notes
I used both weight and volume measures to test this recipe. Three cups (450g) of chopped apples turned out to be approximately five to six Red Prince apples.Apple crumble bars will keep on the counter at room temperature, stored in a container with a lid, for two days. I, however, prefer to keep them in the refrigerator. Stored in the fridge the bars will keep for up to one week.These bars freeze well. I like to wrap individual bars gently but tightly with foil to store in the freezer. To thaw, simply leave the bars out for 30 to 60 minutes at room temperature, or warm them in a microwave or toaster oven until heated through.Apple crumble bars are also delicious served warm topped with whipped cream or ice cream.
SUBSTITUTIONS
We love the rich nutty flavour of rye flour, however, regular all-purpose flour, whole wheat flour, or spelt flour can be substituted.Try replacing half of the cinnamon with cardamom. Homemade chai spice is also a great addition to this recipe.Use a good quality dairy-free butter to make vegan apple crumble bars.