Mix the flour, yeast and 2 tsp salt in a big bowl. Make a well in the centre and pour in the milk. Mix with a wooden spoon, then your hands, to a soft dough. Knead for 10 mins, then put back in the bowl. Lightly cover with oiled cling film and leave somewhere warm-ish until doubled in size – about 30 mins.
Tip the dough onto a lightly floured surface and knead in most of the cheese. Dust a large, flat baking sheet with flour. Shape the dough into 12 round buns and arrange on the sheet with a 2-3cm gap between each. Loosely cover with another sheet of lightly oiled cling film and leave to prove until nearly doubled in size.
Heat oven to 200C/180C fan/gas 6. Mix the 5 tbsp flour for the crosses with the Parmesan and 5 tbsp water. Spoon into a disposable piping bag and pipe a line along each row of buns, then repeat in the other direction to make crosses. Scatter with the remaining cheddar and bake for 20-25 mins until golden. To reheat from frozen, warm in a low oven before serving.