Blueberry Crumb Bars (Gluten Free)

These gluten free blueberry crumble bars are super easy to make and they work great with both fresh and frozen blueberries. The combination of the buttery, melt-in-the-mouth lemon shortbread with the juicy, jammy blueberry filling is delicious and you’d never know that they’re both gluten free and sugar free.

Lemon Shortbread:
½ cup + 2 Tbsp. Monk Fruit Sweetener with Erythritol (Granular) (125 g)
1 lemon, freshly zested, organic unwaxed lemons, if possible
1¼ sticks unsalted butter, softened (140 g)
1 tsp. vanilla bean paste or 2 tsp. pure vanilla extract
2½ cups plain gluten-free flour blend (300 g)
¾ tsp. xanthan gum, omit if your gluten free flour blend already contains it
½ tsp. sea salt

Blueberry Filling:
¼ cup + 2 Tbsp. Monk Fruit Sweetener with Erythritol (Granular) (75 g)
1 lemon, freshly zested, organic unwaxed lemons, if possible
4½ cups fresh or frozen blueberries, if frozen unthawed (600 g)
1½ Tbsp. cornstarch (10 g)
1 Tbsp. lemon juice, freshly squeezed (15 g)
1 tsp. vanilla bean paste or 2 tsp. pure vanilla extract

Preheat an oven to 375°F (190°C/170°C fan, Gas Mark 5). Adjust the oven rack to the lower middle position. Line a 9" (23 cm) square baking pan with parchment paper. I recommend leaving some parchment/baking paper overhang, as that will help with removing the crumble bars from the pan later on.

Lemon Shortbread:
Add the sugar and lemon zest to a large bowl, and use your fingertips to rub the zest into the sugar. This helps to release more essential oils from the zest and it will make your crumble bars even more fragrant.

Add the softened butter and vanilla and mix well with a wooden spoon or rubber spatula until combined. Don’t cream or aerate the mixture, as that can make the shortbread too delicate and crumbly (note the absence of any raising agents for the same reason).

In a separate bowl, whisk together the gluten-free flour blend, xanthan gum and salt.

Add the dry ingredients to the butter-sugar mixture and mix well until it starts clumping together. Then, give it a knead until you get a fairly crumbly cookie dough. Set aside until needed. Because it's gluten-free, you don't need to worry about over-working the shortbread dough.

Blueberry Filling:
Add the sugar and lemon zest to a large bowl, and use your fingertips to rub the zest into the sugar. This helps to release more essential oils from the zest, and it will make your blueberry filling even more fragrant.

Add the (fresh or frozen) blueberries to the lemon sugar along with the cornstarch, lemon juice and vanilla and toss everything together until evenly combined. Especially if you're using frozen blueberries, it's best to prepare the filling just before you assemble the crumble bars. You don’t want the filling to stand around at room temperature for too long - otherwise, the blueberries will start to thaw and release their juices, which can make the bottom shortbread crust a bit soggy, something you definitely want to avoid.

Assembly:
Press about ⅔ of the shortbread cookie dough (~ 390 g) into the lined baking pan. Smooth it out into an even layer, this is easiest done with a small offset spatula.

Arrange the blueberry filling on top of the shortbread base in an even layer.

Crumble over the remaining ⅓ of the shortbread cookie dough, making sure that you get a fairly even coverage but allow some of the blueberry filling to peek through.

Bake for about 50-55 minutes (for fresh blueberries) or 60-65 minutes (for frozen blueberries), or until the crumble is light golden brown and you can see the juices in the filling visibly bubbling through the crumble topping (not just around the edges but also in the centre).

To Serve:
Allow the bars to cool completely to room temperature before you remove them from the baking pan and slice them into individual portions. For extra nice slices, I recommend chilling the crumble bars in the fridge for at least 30 minutes before you cut into them. You can also serve these warm with a scoop of ice cream on top - just note that they're much more delicate when they're warm, so they're more likely to crumble when you cut them.

Storage:
These crumble bars keep well in a closed container in a cool, dry place or in the fridge for about 3-4 days. Note that the crust and crumble will soften slightly with time.

Makes 12 servings.