350g gluten free self-raising flour, plus more for dusting
¼ tsp salt
1 tsp gluten free baking powder
85g cold butter, cut into cubes
150g pot lactose free full-fat yogurt
4 tbsp full-fat lactose free milk
250g cooked new potato, sliced
1 tsp chopped rosemary, plus extra small sprigs
50g Parmesan (or vegetarian alternative), grated
85g Gruyère, half diced, half grated
Heat oven to 220C/200C fan/gas 7.Put the gluten free flour, salt and baking powder into a food processor, then whizz in the lactose free butter until it disappears.
Tip into a large bowl, then make a well in the middle. Warm the lactose free yogurt and milk together in a microwave for 1 min or in a pan; it should be hot and may well go a bit lumpy-looking.
Tip into the bowl and quickly work into the gluten free flour mix using a cutlery knife. As soon as it's all in, stop.
Turn the dough onto a floured (gluten free) surface, bring it together with floured hands, then press out to a large rectangle.
Scatter over the potatoes, chopped rosemary, some of its oil and most of the cheese. Knead a few times, shape into a round, then lift onto a floured baking sheet.
Score the top, scatter with the rest of the cheese, poke in a few rosemary sprigs, then drizzle with the remaining oil. Bake for 25 mins until risen, golden and sizzling around the edges. Best eaten just warm.