How to Make It
In a small bowl, whisk the fish sauce with the lime juice, sugar, garlic, Thai chile and 3 tablespoons of water until the sugar dissolves.
In a large bowl, whisk the cornstarch with the flour, cayenne, baking powder and 2 teaspoons of salt. Whisk in the beer. In a medium bowl, beat the egg white until stiff peaks form. Using a rubber spatula, fold the beaten egg white into the batter.
In a large saucepan, heat 2 inches of canola oil over moderately high heat until it registers 350° on a deep-fry thermometer. Set a rack on a baking sheet. Working in 3 batches, dip the cauliflower florets in the batter and fry until golden, 3 to 5 minutes per batch. Transfer the cauliflower to the rack to drain.
In a large serving bowl, toss the fried cauliflower with the mint, jalapeño and a pinch of salt. Serve right away, with the dipping sauce on the side.