Gluten-Free Apple Crumble Bars (Psyllium Husk Version)

The psyllium experiment on a fall favorite: shortbread cookie base, cinnamon apples, oat and pecan crumble. In this version the cookie base is built on a flour blend without xanthan gum, and psyllium husk powder takes over the binder's job, with a spoonful of water to feed it and a short rest before the dough is pressed into the pan.

Prep Time 15

Cook Time 50

Resting Time 15

Total Time 1 20

bars

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Cookie base (reserve 1/3 cup of the dough for the topping)

1 1/2 cups gluten-free flour blend WITHOUT xanthan gum 210 g; the psyllium replaces it, see Notes
2 tsp psyllium husk powder 6 g; see Notes if using whole husks
1/3 cup cane sugar 67 g
1/4 tsp salt
8 Tbsp butter or dairy-free butter 113 g, softened, cut into tablespoons; dairy-free keeps the bars vegan
1 Tbsp cold water only if the dough will not come together, see Method

Crumble topping

1/3 cup reserved cookie-base dough
2 Tbsp packed brown sugar 25 g
1/3 cup pecans 35 g, finely chopped
1/4 cup gluten-free old-fashioned rolled oats 20 g

Apple cinnamon filling

3 cups chopped apples about 375 g, peeled and cut into 1/4 to 1/2 inch pieces, about 3 medium apples
1 1/2 tsp ground cinnamon

Heat and line. Preheat the oven to 375 degrees F. Line an 8-inch square baking pan with parchment paper, leaving an overhang so you can lift the finished bars straight out of the pan.
Make the cookie base. In a large mixing bowl, whisk the flour blend, psyllium husk powder, cane sugar, and salt together first, so the psyllium is evenly distributed. Combine on low speed for about 5 seconds (stand mixer or hand mixer). Add the butter one piece at a time and keep mixing until a dough forms and pulls away from the sides of the bowl, about 2-3 minutes. If the dough stays dry and sandy, sprinkle in the cold water and mix again; psyllium needs that drink, and a shortbread gives it almost nothing.
Rest the dough. Let the finished dough rest for 10-15 minutes before pressing. The psyllium finishes hydrating in this rest, and the base holds together better for it. Do not skip it.
Reserve and press. Measure out 1/3 cup of the rested dough and set it aside for the crumble. Press the remaining dough into an even layer in the prepared pan with your hands.
Bake the base. Bake for 15 minutes, rotating the pan halfway through, until the edges begin to brown.
Make the filling. While the base bakes, stir the chopped apples and cinnamon together in a small bowl.
Make the crumble. While the base bakes, put the reserved dough back in the mixing bowl with the brown sugar, pecans, and oats. Mix with a mixer, a pastry cutter, or your hands until combined and crumbly. Set aside.
Assemble. Pour the cinnamon apples over the hot cookie base and spread them evenly. Sprinkle the crumble over the top, pinching it between your fingers to make small clumps. Do not press the crumble into the filling.
Bake the bars. Bake for 22 minutes. Cover the pan with foil and bake 10 minutes more. Turn the oven off and leave the covered pan in the oven for 5 more minutes; the apples finish baking without the topping over-browning.
Cool and cut. Let the bars cool completely in the pan. Lift them out by the parchment onto a cutting board and cut into 16 bars.

Total time is plus cooling; the bars must cool completely before cutting.
Not yet test-baked, trial-run checklist: (1) Does the base come together without the water, and hold an even pressed layer? (2) Does the cooled base cut cleanly into bars that hold together (the result psyllium is here to improve), or is it as crumbly as the original? (3) Does the base stay crisp like a shortbread, or does the psyllium soften it? That is the main risk in a low-moisture dough. (4) The crumble gets its psyllium only through the reserved base dough; check the topping still bakes up crisp, not soft.
Use a flour blend without xanthan gum in this version. Psyllium and xanthan are both binders; running the blend xanthan and the psyllium together is how a crumb turns gummy.
Using whole psyllium husks? Use 1 Tbsp and grind them to a fine powder first, for the smoothest crumb.
Store in the refrigerator for several days.