Preheat your oven to 160C Fan / 180C and prepare a 9x9 inch square tin with non-stick baking paper.

In a bowl cream together your softened butter and caster sugar until light and fluffy.

Mix in your flour and xanthan gum until it starts to come together. Once it does, get your hands it to finish bringing it all together into a dough - it's fine if it is a little crumbly.

Press your dough down into your prepared tin. I use my hands to evenly push it to the edges. Then prick all over with a fork.

Bake in the oven for 20-22 minutes, until the edges are starting to go golden.

Whilst your base is in the oven, prepare your filling - you want to pour it on as soon as the base comes out so prepare this straight away so you're ready! In a large bowl mix together your sugar and lemon zest so that the zest is evenly dispersed. Then, stir in your flour.

Next add in your lemon juice and eggs. Mix until completely combined.

Once your base is cooked, remove from the oven, wait a couple of minutes and then pour your lemon mixture over the cooked base. Put straight back into the oven and bake for a further 20-22 minutes or until the mixture basically doesn't wobble/jiggle anymore.

Allow to cool fully at room temperature and then pop in the fridge to chill. This should be for no less than 2 hours, but I tend to leave mine overnight.

Once ready, remove from the tin and cut into even squares with a sharp knife. At this point, you could just dust with icing sugar and eat without the meringue... but the meringue is the best bit!

Place your egg whites and cream of tartar into a stand mixer (or use an electric hand mixer) and mix until they turn white, frothy and just past soft peaks.

Place your water and sugar into a saucepan and heat them up until it reaches around 118C (no hotter than 120C). I'd recommend using a digital cooking thermometer for this - but if you don't have one, it's a little past boiling point.

Once your sugar syrup has reached the right temperature, remove it from the heat and with the mixer still going, gradually and slowly pour the sugar syrup into the egg whites. (If you are using an electric hand mixer you will need to mix at the same time as slowly pouring the syrup in... or ask a friend to help!!)

Once the sugar syrup is all in, you can turn the mixer up and mix for just under 10 minutes. The mixture will be thicker, glossy, smooth and also should have cooled down in this time. It's now ready to use.

Place your cooled Italian meringue into a piping back with a large star nozzle and pipe a tall swirl into each of your lemon squares - you could just spoon it on top too if you prefer!

Use a blow torch to get a little colour onto the meringue if you like. (the meringue is already cooked from the hot sugar syrup so this is only for looks!