Cut the greens from the cauliflowers. Set the pale, thin leaves that were closer to the flower to one side. Cut any longer than 6cm (2 inches) in half at the width, and any stems thicker than 1cm (1/2 inch) in half lengthways. Wash well. Cut the core into 2-3cm (1-inch) dice and separate the florets using your hands, cutting any much bigger than a mouthful in half.
Cook the pasta in a large saucepan of rapidly boiling, well-salted water for 1 minute less than packet says. With 90 seconds to go to the end of the adjusted cooking time, add the thick leaves, then once the time is up, drain everything through a colander.
Meanwhile, place a heavy-bottomed frying pan over a medium-high heat in preparation for browning the cores and florets (you’ll almost certainly need to do this in two batches).
Roughly chop the anchovies and tip half the flavored oil into the pan. Fry half of the florets and core for 2 minutes without touching, so the edges turn a little golden. Add half the butter, half the anchovies and half the garlic to the pan. Fry for 2 minutes more, stirring occasionally. Set aside the contents of the pan on a plate or large bowl and repeat with the remainder of the cauliflower.
Set the oven to 450° F. Decant the crème fraîche into a roasting tin or ovenproof dish about 25 x 15cm (13 x 9 inches) in area and at least 6cm (about 3 inches) deep. Add 200ml (a little less than 1 cup) tepid water and stir into the creme fraiche until fully combined. Add the mustard, lemon zest and juice, Parmesan, half of the cheddar and lots of black pepper. Stir well. Transfer the cauliflower florets and core to the mix. Then add the drained pasta and all the greens and mix so everything is glossed with the sauce. You will need to use two implements at this stage to mix things around.
Ensure even distribution of the greens, and that many of them are towards the top of the dish. Drizzle generously with oil and sprinkle the remaining cheese on top. Bake for 20 minutes, or until the top is golden, crisp and bubbling.