Preheat the oven to 375°F.
Make the pancetta and mint topping: Place the bread, pancetta, and mint leaves in a shallow roasting pan just large enough to hold everything in a single layer. Drizzle the olive oil over the top, tossing to coat everything evenly. Bake the topping, stirring occasionally until browned and crisped (20-25 minutes). Remove the pan from the oven and set aside.
Make the pea soup: Heat the butter or olive oil in a large, heavy pot over medium heat. Add the leeks and cook, stirring frequently until quite soft (8-10 minutes). Add the slivered mint and cook until it begins to wilt (about 30 seconds). Add the peas and chicken stock or broth and let come to a boil. Reduce heat to medium, season with salt and pepper to taste, and let simmer until peas are tender (10-12 minutes). Stir in the cream and let simmer until heated through (about 5 minutes).
Using an immersion blender, puree the soup in the pot until very smooth. Taste and add more salt/pepper if needed (if you don’t have an immersion blender you can also puree the soup in batches in a blender).
Ladle the hot soup into soup bowls and scatter a generous handful of pancetta and mint topping over each. Spoon a generous dollop of sour cream, creme fraiche, or yogurt into the center of each serving, then drizzle a swirl of extra virgin olive oil on top. Serve hot.
Words by Tom Dott / Recipe from Sarah Leah Chase’s New England Open-House Cookbook: 300 Recipes Inspired by the Bounty of New England