Cook the pasta until al dente. Reserve 1 cup of pasta water. Drain, rinse, and set aside.
In a large skillet, melt the butter then add garlic and cook until fragrant. Pour in the heavy cream and stir until mixture thickens. Add lemon zest, 1 tbs. lemon juice and 1 tsp. tarragon. Season with salt and pepper.
Add the pasta to the cream sauce and toss. If too thick add some pasta water to the pan.