Melt butter in a large skillet on medium heat. Add chicken breasts and cook until done & lightly browned on both sides. Remove Chicken to a warm, covered serving platter.
Stir flour into the pan drippings with a whisk. While whisking, gradually add chicken broth, wine and light cream. Stir and cook until the sauce thickens & bubbles. Stir in the mustard.
Turn heat to low, return the chicken to the skillet, add taragon and rosemary, cover & heat for about 10 minutes, making sure the sauce does not get too thick. (If it does, add more wine or chicken broth).
Garnish with tomatoes and some fresh rosemary sprigs.