Celeriac rosti

I don't go in for brunch in a big way. It's nice to have some things standing between you and the long slide to egregious self-parody, after all. That said, I'm unlikely to be out of bed before 10 am on a sunday, and so the first food into the face hole is, accordingly, Brunch By Default.When I can be bothered faffing about a bit, rather than just clawing bacon into my seething, hungover maw, these celeriac and potato rosti are just the ticket.Stick a poached egg and a little hollandaise on top for maximum bourgeois brownie points:The celeriac makes what is basically a posh hash brown a little unusual, adding a depth and sweetness that really works.

Ingredients:

Rosti:

• Celeriac - 450g
• Potatoes - 150g
• Onion - one medium
• Flour - 2 tbsp
• Egg - one
• Parsley - a good pinch
• Salt & pepper

...and an optional egg to go on top, poached.

Hollandaise:

• White wine vinegar - 50ml
• Water - 50 ml
• Butter - 200g
• Eggs - 3
• Tarragon - a pinch

Serves four as a starter/lunch/brunch.

Instructions:

Trim and peel the celeriac. The recipe uses around half a standard sized one. Grate the celeriac, potatoes, and onion, and put the mix into a colander or sieve or something. Squeeze out as much of the liquid as you can, then add the flour, egg, parsley, and any other seasoning that takes your fancy. Heat the oven to about 150c.Mix everything thoroughly, and then shape the mix into either four large or eight small patties. Set them frying in plenty of oil on a medium heat for at least five minutes on each side, probably closer to eight, until they're a nice golden brown.They're not the most robust, so be careful when you turn them, as they can collapse. You can make the shape nicer by using one of those ring mold thingies if you like. Or a metal pastry cutter, at a pinch.When they're a good colour, remove the rosti to a medium oven (say, 150c) to finish for ten minutes or so, and ensure they're cooked through.Now make the hollandaise if you're using it. Also, you should look up a more thorough guide than mine. This is a bit seat of the pants. The BBC one is good, and I've always liked the one in How To Cook Better.Anyway here's what I do:Mix the water, vinegar, and tarragon, and gently reduce the volume by half. This is to concentrate slightly, and let the tarragon infuse. Separate the eggs, keeping the yolks. Melt the butter. Set up a water bath, with a bowl over a pan of hot (but not quite boiling) water. In the bowl, whisk together the egg yolks, and 2 teaspoons of the vinegar mix.Whisk this briskly and get it to a slightly foamy consistency. Do this over the hot water, removing it periodically to stop it all overheating. If the sauce overheats it will misbehave and split. Start adding the butter, just a little at a time, whisking as you go. The sauce will gradually emulsify and thicken as you go, and you'll be able to get a bit more bold with the butter. Eventually it'll be thick and glossy.To serve, poach an egg to go on top of each of the rosti, and top with hollandaise.The hollandaise can be a bit tart if you're not careful with the vinegar (indeed, some recipes just use wine) but that works well with the richness of the yolk and the slight sweetness of the celeriac.