Preheat oven to 220°C/200°C fan/gas 7.
Cook the pasta according to pack instructions, until al dente.
While the pasta cooks, make the cheese sauce: In a saucepan, melt the butter over a medium heat, then add the flour and stir continuously for around 2 mins, until it turns golden. Grab a whisk and add the milk gradually; keep whisking the whole time, until the sauce starts to thicken (about 3-5 mins). Remove from the heat and add the gruyère, 50g of the cheddar, the parmesan. Season to taste and set aside.
Once the pasta is ready, drain and transfer into a large ovenproof dish. Pour the cheese sauce over then add the tomatoes and the frankfurters, stir. Scatter the remaining 50g cheddar and bread crumbs on top.
Oven cook for 15 mins, until bubbling. Remove, drizzle with extra virgin olive oil.
