For the balsamic Dijon sour cream: Stir together the sour cream, mustard, honey, vinegar and salt in a small bowl. Set aside.
For the latkes: Whisk together the egg whites and lemon juice in a large bowl. Add the Brussels sprouts, onion and garlic and stir to combine. Stir in the flour, 3/4 teaspoon salt, some black pepper and a few pinches of red pepper flakes.
Line a plate with paper towels. Heat a thin layer of oil in a large skillet over medium-high heat until shimmering. Scoop an eighth of the mixture (about 1/2 cup) into the skillet and use a spatula to pat it out into a flat pancake, about 1/2-inch thick. Cook until browned, 3 to 4 minutes on each side. Repeat with the remaining batter.
Remove to the paper towels, sprinkle with salt and serve with the balsamic Dijon sour cream and lemon wedges on the side.