A note about nettles: Yes, they sting, due to hollow hairs on the leaves and stems that inject histamine and other chemicals into the skin when touched. Fortunately, soaking the leaves and stems in water, or cooking them, nullifies the problem, but be sure to handle stinging nettles with gloves before thoroughly washing or cooking them.
2 cups whole milk
1½ cups heavy cream
6 tablespoons fresh lemon juice, plus zest of 1 lemon
4 tablespoons butter
1 pound baby turnips with green tops, chopped
2 leeks, white and light green parts only, chopped
½ pound fresh stinging nettle tops, soaked and rinsed thoroughly (handle with gloves)
4 cups good-quality chicken stock
Extra-virgin olive oil
Freshly cracked black pepper
Great chickweed (optional)
1. In a medium saucepan over medium-high heat, bring milk, 1 cup cream, and ½ teaspoon salt just to a boil, stirring occasionally to prevent milk from scalding. Remove from heat. Add 3 tablespoons lemon juice, stirring gently so as not to break up the curds. Let stand for 4 minutes. Meanwhile, place a double layer of cheesecloth in a sieve set over a bowl. Pour ricotta mixture into cheesecloth, reserving the whey that drains into bowl. Gather ends of cheesecloth, tie off with twine, and hang to drain over a bowl for about 2 hours.
2. In a large heavy pot over medium-high heat, melt 2 tablespoons butter. Reduce heat to medium; add turnips and leeks and cover pot. Let vegetables sweat, stirring occasionally, for about 15 minutes. Add nettles and let them wilt, stirring occasionally, for about 5 minutes. Pour in stock, 1 cup of the reserved whey, and salt to taste; cook for 10 minutes more to allow flavors to marry. Stir in remaining 3 tablespoons lemon juice. Using an immersion blender, puree soup until smooth. (Or, let soup cool then carefully pour into a food processor or blender and puree in batches before returning to pot.) Add remaining 2 tablespoons butter and gently reheat if necessary.
3. Meanwhile, transfer ricotta to a bowl and whisk in remaining ½ cup cream, a few tablespoons at a time, until cheese is somewhat smooth and not too crumbly. To serve soup family style, spoon heaping dollops of ricotta onto surface of soup, then drizzle with olive oil and sprinkle with lemon zest and a generous amount of pepper. Garnish with great chickweed, if desired.