Preheat the oven to 200C/Gas6; put 50g of the cheddar and the butter, flour, baking powder, mustard, cayenne pepper and salt in a food processor and pulse until it forms fine crumbs
Add the 120ml milk, process for a few seconds until the dough forms soft clumps, then tip onto a lightly floured work surface; gather into a soft, not sticky, dough
Roll out the dough on a lightly floured surface; shape into a rectangle about 18cm x 24cm; spread on the Marmite; mix the rest of the grated cheddar with the parmesan and sprinkle most of it evenly over the dough; roll up from one long side to make a fat sausage, then cut into 8 thick slices; arrange them cut-side up on a lined baking tray and brush with milk; sprinkle with the rest of the cheese and bake for 15-20 minutes until risen and golden brown; allow to cool and serve
8 servings