Heat the oven to 200C/180C fan and put a baking tray inside to heat up.
Stir the lemon juice into the milk and leave it to sit for 5 minutes until it looks slightly curdled. This soured milk does the same job as buttermilk at a fraction of the price.
Mix the flour, bicarbonate of soda and salt in a large bowl and make a well in the middle.
Pour in the soured milk and stir with a knife or wooden spoon for about 20 seconds, just until it comes together into a soft, slightly sticky dough. Do not overwork it.
Tip onto a floured surface, shape quickly into a round about 20cm across and lift it onto the hot tray. Cut a deep cross in the top, almost all the way through.
Bake for 30-35 minutes until well risen, golden and hollow-sounding when you tap the base. Cool on a wire rack for at least 20 minutes before cutting.