Recipes for the season: Spring Pea Soup

Ingredients

• 1 Tbsp unsalted butter
• 1 medium onion, peeled and chopped
• Salt
• freshly ground pepper
• 4 cups chicken broth or vegetable broth
• 12 oz frozen petite peas
• 1 medium head romaine lettuce, trimmed and sliced
• Creme fraiche, sour cream or heavy cream for serving