1 ½quartsVegetable stockor frozen vegetable broth, thawed, plus more for thinning
2 ½lbssweet peassheled, or 4 of 10-oz boxes frozen peas
Instructions
Cover and bring 3 cups water to a boil. Remove from heat, add mint, reserving a few sprigs for garnish, and let steep for about 2 hours, until liquid is very flavorful and slightly green. Strain, discarding mint; transfer to 2 ice-cube trays, or an 8-inch square baking pan. Freeze until solid. You may do this step up to 2 days ahead
Meanwhile, melt the butter in a medium saucepan over medium-low heat. Add the chopped onion, salt, and pepper; cook, stirring often, until the onions are soft and translucent, about 8 minutes
Add the stock, cover, and bring to a boil. Reduce heat; simmer, uncovered, 1 hour, until liquid is reduced by half. Prepare an ice-water bath; set aside. Add peas to the stock and cook for about 4 minutes, until are just tender. Remove from heat; transfer to the ice bath. Stir until cold
Working in batches, transfer soup to a blender; process until smooth. Adjust consistency with more stock. Chill until ready to serve
Transfer mint ice cubes from freezer to a blender (if using an 8-inch square baking pan, cut ice into chunks first). Process mint ice cubes until crushed
Place the chilled soup in serving bowls topped with a spoonful of crushed mint ice; garnish with mint sprigs. Serve chilled