Preheat the broiler. Place the red pepper halves, cut side down, in a baking pan and broil 4 to 5 inches from heat until the skins are black and blistered, about 8 minutes. Let cool, uncovered, 10 to 15 minutes. Peel the peppers and place in a bowl, reserving any juices.
In a 3- to 4-quart pan over medium heat, add the olive oil and the onion; stir often until onion is soft, about 5 minutes. Add the garlic and stir until translucent, 1 to 2 minutes. Add the roasted peppers and tomatoes, along with their juices, and the paprika. Bring to a low simmer and cook, stirring occasionally, about 3 minutes.
In a blender or food processor, purée the soup in small batches until smooth. Return purée to the pan and stir in broth and lemon juice. Stir over medium heat until hot. Season with salt and pepper to taste. Ladle into cups or bowls and garnish with a dollop of crème fraîche or plain yogurt and parsley.
Do-ahead tips: Make soup up to 3 days ahead. Store airtight in the refrigerator. Reheat before serving.
Party short-cut: If your guests tend to congregate in the kitchen, leave this roasted red pepper soup over a low flame on the stove and set cups, ladle, and toppings nearby (that's one fewer dish to wash).
Wine pairing: Classic Brut sparkling wine brings elegance to this dish. Alternatively, a dry, fruity rosé is an unexpected match.