Making macaroni cheese is a bit of a juggling act, so it’s easier if you get a few things prepared ahead. Finely grate all the cheeses, keeping them separate. Tear the bread into pieces and whizz in a food processor to coarse crumbs. Mix 25g of the cheddar and one-third of the Parmesan into the breadcrumbs. Toss the rest of the cheeses together and set aside. Thickly slice the tomatoes. Butter a dish, about 30 x 20 x 5.5cm. Heat oven to 190C/fan 170C/gas 5.
Put a pan of water on to boil. Tip the macaroni into the boiling water, stir and bring it back to the boil. Simmer for 8 mins, or cook according to pack instructions, stirring occasionally to stop it sticking. While
this is cooking, start the sauce.
Warm the milk in a jug in the microwave (or in a pan). Melt the butter in a pan (big enough to take the macaroni as well), then stir in the flour. Cook for 1 min, stirring, then take off the heat. Pour in one-third of the warm milk and beat well with a wooden spoon until smooth – it is quite thick at this stage. Add another third – it may go a bit lumpy, but keep beating well and it will go smooth again. Pour in the final third of milk and keep beating until smooth.
When the macaroni is done, tip it into a colander and put it briefly under very hot running water to keep it separate. Drain. Put the pan of sauce back on the heat and cook, stirring, until thickened and smooth. Lower the heat and simmer for about 4 mins until glossy, stirring
every now and then. Remove from the heat
and stir in the cheese and mustard, then beat
in 5 tbsp milk, or enough to give a slack coating consistency. Taste and season (you shouldn’t need much salt). If the macaroni
is sticking at all, put it under the hot tap again,
then stir to separate. Drain well, then gently mix
it into the sauce and stir to coat completely. If necessary, adjust the consistency again with
milk. There should be enough sauce to coat
the macaroni thickly and liberally.
Tip the macaroni cheese into the buttered
dish, scatter over the cheesy crumbs and lay
the tomatoes casually over the top.
Heat through in the oven for 12-15 mins until beginning to bubble around the edges. Grill for
3-5 mins to brown the crumbs. Let it all settle
for 1-2 mins, then serve while still piping hot.