Step 1

Adjust the oven rack to the middle position, pre-heat the oven to 350ºF (180ºC) and line a 9-inch (23cm) square baking pan with parchment/baking paper.Tip: When lining the baking pan, I recommend leaving some parchment/baking paper overhang, as that will help with removing the crumble bars from the pan later on.

Step 2

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

Step 3

Add the softened butter and vanilla, and mix well with a wooden spoon or rubber spatula until combined. Tip: 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).

Step 4

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

Step 5

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.Tip: Because it's gluten free, you don't need to worry about over-working the shortbread dough!

Step 6

Press about ⅔ of the shortbread cookie dough (about 370g) into the lined baking pan. Smooth it out into an even layer, this is easiest done with a small offset spatula.

Step 7

Spread the raspberry jam on top of the shortbread base in an even layer.

Step 8

Scatter over the fresh raspberries – they won't be packed closely together, just make sure that they're fairly evenly distributed.

Step 9

Crumble over the remaining ⅓ of the shortbread cookie dough (about 190g), making sure that you get an even coverage.

Step 10

Bake at 350ºF (180ºC) for about 40-45 minutes or until the crumble is light golden brown and you see the jam bubbling around the edges.

Step 11

Allow the bars to cool to room temperature before removing them from the baking pan (with the help of the overhanging parchment/baking paper) and slicing them into individual portions.Tip: 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. For neater slices, cut them once they've cooled completely to room temperature and then re-heat them briefly in the microwave.

Step 12

The gluten free lemon raspberry 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.