Bring the stock to a simmer in a medium pot, and then set aside. Melt 1 1/2 tablespoons of the butter in a large saucepan and cook the shallots until soft, stirring with a wooden spoon. Add the rice and stir until translucent, about 4 minutes. Stir in the wine and simmer until reduced to almost dry. Ladle the stock into the rice slowly, stirring until it disappears each time. Remove the saucepan from the heat and add the mascarpone and Parmigiano, stirring until well blended.
Prepare a bowl of ice water. Bring a pot of salted water to a boil. Blanch the asparagus tips and stems until al dente, and then dip in ice water for 2 to 3 seconds. Place the stems in a food processor and add the creme fraiche and lemon juice. Puree the mixture until thick and smooth. Saute the tips in the melted butter over medium-high heat until well coated, about 1 minute.
To serve, place a small amount of puree into a bowl, spoon some risotto over, and garnish with asparagus heads and fresh melissa, hyssop and garlic. Sprinkle sea salt on top to taste.