There aren’t any strict rules you must follow, but try to keep them chunky and retain some of the natural shape of the vegetable, where possible. For example, cut round vegetables into thin wedges and long vegetables into batons or strips. Here are a few useful suggestions.• For cauliflower and broccoli, divide into medium florets• For beets, peel and cut into 1/8-inch-thick slices or wedges• For potatoes and sweet potatoes, leave the skin on and cut into 1/4-inch-thick slices• For Jerusalem artichoke, carrot, parsnip, salsify, turnip and celeriac, peel and cut into 3/8-inch-thick sticks, not too perfect• For baby leeks, just trim off the green ends
Before you start frying the vegetables, prepare a large plate lined with paper towels. Scatter some cornstarch for coating the vegetables on another plate. Place the batter ingredients – the flour, the 1/2 cup of cornstarch, sparkling water, grapeseed oil, and salt – in a bowl and whisk well to get a smooth, runny mix. Add some chile flakes for heat.
Pour the frying oil in a medium saucepan and place on high heat. Once very hot, turn the heat down to medium. When frying the vegetables, the oil should be hot enough so you get a good sizzle but not so hot that they burn.
Take each piece of vegetable and toss it in the cornstarch. Shake to remove any excess, then dip it in the batter. Lift and shake again, then carefully put into the oil. Deep-fry four or five pieces of vegetable at a time. As they fry, turn the pieces over to color evenly. Soft vegetables like leeks should take about 1 minute to cook, harder ones like beets 2 minutes or more. When frying, occasionally remove any burnt bits that float in the oil. As they cook, transfer the vegetables onto the paper towels and keep warm.
When all the vegetables are cooked, serve them at once, with the dipping sauce on the side.