01 - Melt the butter in a large saucepan over medium heat. Add the chopped onion and cook for 4–5 minutes, stirring until translucent but not browned.
02 - Add the minced garlic and cook for 30 seconds, until fragrant.
03 - Stir in the peas and vegetable broth. Bring to a simmer and cook for 5–7 minutes (3–5 minutes if using frozen peas), until peas are tender and bright green.
04 - Remove from heat. Add the mint leaves, crème fraîche, and milk (or cream). Stir to combine.
05 - Using an immersion blender (or working in batches with a countertop blender), purée the soup until smooth and creamy.
06 - Stir in lemon zest and juice. Season with salt and pepper to taste.
07 - If desired, pass the soup through a fine-mesh sieve for an extra-silky texture.
08 - Ladle soup into bowls. Swirl each serving with a spoonful of crème fraîche and garnish with extra mint leaves.