In a heavy bottomed large pot, pour the oil to half full over medium heat. Bring the oil to 375 degrees F.
Meanwhile, in a medium bowl add the egg whites and the sparkling water and beat well to combine. Take a handful of smelt and immerse them in the egg white mixture. Remove the fish and roll in the flour. Use a hand strainer or a colander to shake off excess flour.
Make sure your oil is hot. Careful place the coated fish in the oil and fry for about a minute or until lightly golden brown. With a slotted spoon, transfer the fried fish to a paper towel lined sheet pan. Continue to fry all the fish in batches. On the last batch, add the rosemary.
Place the fried smelts on a warm serving platter. Season with salt to taste. Add the fried rosemary and some lemon wedges. Serve immediately.
Tomato 'Nduja Sauce
Makes about 3 cups
Heat the olive oil in a medium saucepan over medium-high heat. Add the garlic and brown on both sides, about 2 to 3 minutes. To avoid splattering, reduce the heat to low and add the tomato puree. Turn up the heat and bring to a simmer. Add the ‘nduja and stir well to combine. Cook until slightly reduced, 10 to 15 minutes. The sauce can be refrigerated for up to 3 days. Reheat before using.