Inspired from Gratin de chou fleur
Comment: You can replace the cauliflower with broccoli. The recipe remains the same, but cook the broccoli in salted water a little less, it should remain firm. You should also run it under cold water once cooked to keep it green. Not a big issue in a gratin, but why not making it look better.
For some large cauliflowers, the amount of béchamel can be up to doubled! (in this case, the dish was 8" x 8" and full and the cauliflower was 900 g before cutting into florets).
1 cauliflower (or 2 broccolis) ~750g
2 white tablespoons vinegar
30 g butter
30 g flour (same as the butter)
4 dl milk
150+ g (7 oz) grated cheese (gruyere or other you like).
Put the little bouquets of cauliflower in salted boiling water (with the vinegar) for 5 to 10 mn until cooked (test with a pointy knife).
Meanwhile prepare a "roux" with the butter and flour: melt the butter, add the flour and stir until smooth. Cook for an additional 2 to 3 mn.
Remove the pan from the heat and add the cold milk while stirring.
Return the pan to the heat and bring heat up while stirring to obtain a smooth béchamel.
Add salt, pepper and grated nutmeg.
Remove the pan from the heat and add the grated cheese. Keep some of the cheese for the last step.
Place the cooked cauliflower in a buttered gratin dish.
Pour the sauce over, evenly, and sprinkle some grated cheese on top.
Place in pre-heated oven to 180C (360F) for ~30 mn, near the top (until nice and golden).
A good idea is to place the oven on broil for the last 5 mn (depending on the oven).