In a small bowl whisk together 
2 tbsp. grainy Dijon mustard
1 tbsp. white or red wine vinegar
1 tbsp. liquid honey 
generous pinches of salt & pepper

While risking continuously, drizzle in
1/4 cup of olive or vegetable oil. 
Pour over 4-6 chicken breasts & marinade for 1 hr. in the frig. 
Then barbecue & can brush remaining marinade over chicken while barbecuing if desired. 
Can double marinade if cooking more chicken.