This bountiful spring vegetable soup boasts a rich, satisfying flavor thanks to a variety of ingredients. The combination of Parmigiano-Reggiano rind and vegetable umami imparts a delicious, salty richness, while the use of curly leaf spinach adds a fresh, vegetal taste that sets it apart from baby spinach. For those who enjoy the savory taste of Parmigiano-Reggiano, it's worth noting that the rinds can be stored in the freezer for several months.