First make your batter. Smash up the cumin and mustard seeds, chiles and peppercorns in a pestle and mortar until you have a powder. Put the flour into a mixing bowl and stir in the ground spices and the turmeric. Pour in most of the beer and whisk gently. Check the consistency - you want it to be the thickness of heavy cream. If it's too thick, whisk in the rest of the beer. Don't worry too much about having little lumps in the batter, as they'll just become nice crunchy bits when you start frying. Season with sea salt and put aside.
Trim the bottom of the stalk and break the cauliflower into bite-sized florets. Slice up the stalk into 1-inch pieces - this way it will all cook at the same rate. Wash the cauliflower, drain it and pat dry with kitchen towels. Place the cauliflower pieces in a bowl and dust with a little flour.
Pour the oil into a deep saucepan - you want it to be about 4 to 5 inches deep - and heat it to 350 degrees F. If you don't have a thermometer don't worry, just drop a piece of potato into the oil. When it floats to the surface and starts to sizzle, the oil will be at the right temperature so remove the potato from the pan.
Shake any excess flour off the cauliflower. One by one, dip the pieces into the beer batter, then carefully place them in the hot oil, moving them away from you as you do so. Make sure you stand back so you don't get splashed. It's best to fry them in batches so you don't overcrowd the pan (but serve them as soon as each batch is ready). Each time a batch of cauliflower is nearly ready, add some battered parsley leaves to the pan and fry for 40 seconds (you want to serve them scattered over the fritters). Fry the pieces gently, turning them a couple of times with a slotted spoon. When they're browned and crisp, lift them out of the oil, allowing any excess to drip back into the pan, and drain on kitchen towels. Dust with sea salt and squeeze over a little lemon juice.
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Recipe Excerpted from JAMIE AT HOME by Jamie Oliver. Copyright (c) 2008. Published in the U.S. by Hyperion. All Rights Reserved. Available wherever books are sold. www.jamieoliver.com