365 kcal per person
No kJ per person given
1 Preheat the oven to 200˚C/180˚C fan/gas mark 6.
2 Melt the butter in a saucepan over a medium-high heat. Whisk in the flour and keep whisking for one minute. Whisk in the milk, a little at a time.
3 Bring to the boil, then reduce the heat a little and simmer for two minutes. Stir in the mustard along with three-quarters each of the Cheddar and Parmesan.
4 Meanwhile, cook the parsnips and carrots in a large pan of salted boiling water for 7-8 minutes until just tender, adding the leeks for the last three minutes. Drain the vegetables well, then tip them into a large baking dish. Scatter over the beetroot and rosemary, then pour the cheese sauce over everything.
5 Sprinkle the breadcrumbs over the gratin, along with the remaining cheeses. Bake in the oven for 18-20 minutes until the breadcrumbs are golden and the sauce is bubbling around the edges.