Heat olive oil in a large skillet or saucepan over medium heat.
Add fennel and onion. Cook 5–7 minutes until softened and fragrant.
Stir in carrots and garlic. Cook another 3 minutes.
Pour in broth. Bring to a simmer and cook 15 minutes, until carrots are very tender.
Carefully transfer mixture to a blender (or use immersion blender). Blend until smooth and creamy.
Return sauce to pan. Stir in cream and butter. Season with salt, pepper, and a squeeze of lemon juice.
Toss cooked ravioli in the sauce, garnish with fennel fronds or parmesan, and serve warm.