In a small saucepan, combine the wine, shallot, and thyme and bring to a simmer over medium-high heat. Boil until reduced by half, about 4 minutes. Add the vinegar and continue to simmer, stirring and scraping the sides of the pan occasionally with a heat-resistant rubber spatula, until the liquid is reduced to about 2 tbsp, 4 to 5 minutes.
Add the butter and start stirring it around in circles with a whisk, a fork, a wooden spoon, or anything that lets you “stab” the hunk of butter so that you can move it around easily. The butter will start to melt and the mixture will bubble and boil around the edges. The melted butter should look creamy, rather than melted and oily. Keep stirring and blend
Balsamic-Red Wine Reduction
For meaty fish such as halibut or salmon, it’s gutsy enough to drizzle over medallions of beef or pork, too.
3/4 cup/180 ml fruity (but not oaky) red wine such as Pinot Noir, Syrah, or Tempranillo
1 tbsp minced shallot
1 fresh thyme sprig
1/4 cup/60 ml balsamic vinegar
1/2 cup/115 g very cold unsalted butter in one piece, plus 1/2 tbsp if needed