Preheat your oven to 220ºc/200ºfan, and place a lined tray in the oven to preheat.
Tip the self-raising flour, sea salt, baking powder, ground cinnamon, light brown soft sugar and cold and cubed unsalted butter into a large bowl.
Rub the mixture together with your fingertips until it resembles bread crumbs
Heat the full-fat milk in the microwave or on the hob so it becomes warm, but not hot.
Add the milk into the rest of the mixture, along with the lemon juice and stir with a spatula as it'll be very wet at first.
Make sure the dough is mixed well, and add in the chopped apple. Carefully mix together.
Sprinkle some extra flour onto the work surface, and turn the dough out onto it and gently roll it out, or press it down, to be about 4/5cm thick.
Using a 5cm cutter, cut out the scones - you'll have to re-roll the mixture a couple of times to get them all out of the mix.
If you are making your own crumble mix, in a new bowl rub the ingredients together to breadcrumbs now.
Take the tray out of the oven, and put the scones onto it. Brush the top of the Scones with the beaten egg mixture and sprinkle/press on some of the crumble mixture per scone and bake in the oven for 10 minutes.
Leave to cool for at least 10 minutes once they're out so you don't burn yourself. And then, enjoy!
Notes
You could easily make smaller or bigger scones if you wanted, but adjust the baking times accordingly.
These are best on the day of baking, but they will last for two days after.