In a sauce pan reduce the broth on medium-high heat for about 20 minutes or until volume reduces to roughly 1/2 cup, then pour into a bowl and set aside
Whisk in the wine, onion, tomato paste and thyme to the pan, bring to a boil the simmer on medium high for about 8 minutes or until reduced top 1/3 cup.
Add the broth back to the pan, bring to a boil, then reduce to medium-high and simmer for about 7 minutes or until volume reduces to about 2/3 cup
Strain the liquid into a bowl. Whisk the butter into the sauce 1 tsp at a time.
If the sauce isn't thick enough, add corn starch as needed to thicken for use on a burger.