In a medium saucepan, bring frozen peas, 1/4 cup water, and salt to a boil; reduce heat, and simmer, covered, over low heat until peas are tender and the liquid has evaporated, about 5 to 7 minutes. Remove from heat.
Transfer 1 1/2 cups cooked peas to a food processor, and add butter and milk. Puree until smooth. Fold pureed mixture into the remaining cooked peas, and serve.