1. In a large saucepan, melt butter with heavy cream over low heat. Add thyme, garlic, salt, and pepper. Stir in Parmesan over medium heat until melted; this will thicken the sauce.
2. Add pasta to the sauce and stir until pasta is fully coated.
3. To serve, remove thyme sprigs. Add pasta to a large bowl and garnish with fresh tarragon and microgreens.