I've been making this recipe for years. It's very tasty and great with any pasta. My daughter recently emailed me and asked for the recipe so she could serve it to her boyfriend...she said it was really really good!
Cut the chicken breast up in cubes. Melt 1 tbsp. butter in your saute pan and saute the chicken until almost done, leaving some pink in the middle. You will finish cooking this in the sauce.
Add the ground garlic in with the chicken just before you're finished cooking it. Add some of the tarragon leaves. Saute for a second or two and remove the chicken from the pan. Set aside.
Add another tbsp. butter and saute the sliced mushrooms until just done, don't over cook them either. Remove from the pan and set aside.
Add the last two tbsp. butter and melt it. Then add the flour and make a rue. Add the milk and make a thick sauce. Add in the chicken and mushrooms and cook on low for a few minutes. Turn off the heat and cover the pot and set aside.
Cook the pasta according to the package directions.