Snap off tough ends of asparagus and cut on the diagonal into 2 inch pieces.
Place chicken between waxed paper and using a meat mallet or hammer, gently pound to a thickness of 1/2 inch.
Place flour in a shallow bowl or plastic bag. Toss chicken in flour, then shake off excess.
Heat oil in a large frying pan set over medium-high heat. Add chicken to pan and cook, turning occasionally, just until it loses its pink color and starts to brown.
Meanwhile, thinly slice onions and dissolve bouillon in 1/2 c. boiling water.
Add bouillon, wine and mustard to pan, stirring to distribute the mustard. Cover and cook for 3 minutes.
Add asparagus, cover and continue to cook until chicken feels springy and asparagus is as done as you like.
Stir in onions and tarragon.
Remove chicken to a platter.
Turn off heat and stir in sour cream and salt to taste. Pour mixture over chicken.
Great with rice or new potatoes or even over noodles. Only 274 calories per serving! (If you prefer more sauce, double the following ingredients when you're cooking the sauce: bouillon cube, dry white wine, Dijon mustard, dried tarragon and light sour cream. You may need to add a bit more flour to thicken it.) Enjoy!