Leek Gratin with Prosciutto

Rachel Roddy’s instagram (@rachelaliceroddy) photo of celery, lined up in a gratin dish, en route to becoming Jane Grigson’s celery gratin prompted this latest take on a favourite gratin of mine, leeks wrapped in prosciutto. This in turn is based on a French brasserie dish, often made with chicory. Because leeks are tricky to slice once cooked, I always steam them in bite-size pieces and because they are very juicy, cover them in a thick, well-seasoned, cheesy sauce (sweet, springy cheeses like gruyere, emmental or newly discovered Aarewaser work particularly well) that can’t spoil if they leach liquid as the gratin cooks. It’s a useful make ahead dish, the gratinee topping (breadcrumbs and grated Parmesan) added when the sauce has set. I used to always serve it with sprouts and mash but this time it was oven chips (Aunt Bessie) cooked at the same time and frozen petits pois. To extend the dish, just increase the ingredients in proportion. The version in the photo is of a more rustic version made with slices cut from a boiled gammon and equally delicious in a different way.

Serves 2
Prep: 20 min
Cook: 35 min

2 long trimmed leeks (approx 200g)
70g prosciutto

for the sauce:
1 small onion
1 bay leaf
4 black peppercorns
25g butter
1 tbsp flour
300ml milk
150g Gruyere, Emmental or Aarewasser cheese

for the topping:
3 tbsp fresh breadcrumbs
2 tbsp finely grated Parmesan

First job is to flavour the milk for the sauce. So finely chop the small onion and place in a pan with the bay, peppercorns, pinch salt and 300ml milk. Simmer gently for 10 minutes (at least), cover and leave to infuse while you prepare the leeks. Trim the leeks and cut into 5cm approx lengths. Steam for 8 minutes or until tender to the point of a sharp knife. Leave to cool then wrap in prosciutto, probably halving the sheets so you have enough. Line the pieces, join underneath, in a gratin dish. Melt the butter in a clean pan over a medium-low heat, stir in the flour then add the milk through a sieve to catch the onion etc. Stir vigorously as the sauce begins to simmer, adjusting the heat, stirring until it settles into a thick, smooth sauce. Cook for a few minutes while you grate the gruyere. Stir most of it into the sauce, when melted and Vesuvial, spoon it over the leeks to cover. Leave to cool. Mix together breadcrumbs, Parmesan and remaining grueyere and scatter it over the top. Bake at 200C for 20 minutes or until golden, the sauce bubbling at the edges and serve.