Preheat your oven to 180 degrees Celsius and line a 22cm x 10cm loaf tin with baking paper. Set aside.
In a large bowl place your room temperature butter, add the sugar and using hand held beaters cream together. They won't cream like you're used to, instead it will go very grainy and breadcrumb like. Cream together for 1 minute.
Add in the eggs, lemon juice and lemon zest and beat again until you have a light, well incorporated mix.
Place your bowl onto a set of scales, zero them and measure in 210grams of Bobs Red Mill 1:1 flour mix. This is approx 1 + 1/2 cups of flour. Add in the baking powder, bicarb soda and xanthan gum. Use a large spoon to bring together until all the flour is incorporated.
Strain out your tinned blueberries, ensuring your keep the juice for later. Add blueberries into your mixture and mix well. Some blueberries will mush here but it just adds to the flavour and beautiful purple hue. Once the blueberries are roughly distributed spoon mix into loaf pan and smooth out the top.
Place into your preheated oven for 35-40 minutes. You'll be able to tell it's done when the scent of lemon wafts through your kitchen and your loaf has turned a golden hue all over. An inserted skewer into the center will come out clean when it's ready.
Remove from the oven and allow to cool for 5 minutes in it's pan. I know it's tempting, it smells so good, but don't cut it yet! The cake will simply crumble apart at this point, you must let it rest, preferably for a good 1 hour before serving. Transfer loaf to a wire rack, cover with a clean tea towel and allow to fully cool.