Balsamic Glaze with Orange and Rosemary (Reduction)

Excellent for a sautéed pork medallion, salmon or seared scallops. The concentrated balsamic vinegar turns the sauce a lovely, glossy brown, almost like a chocolate sauce. Use a decent vinegar but not an artisanal one. I like Lucini brand, which costs around $10 for a small bottle. That's seems to be a fair price for a good-quality balsamic vinegar to use for cooking, rather than as a condiment.

¼ cup balsamic vinegar
¼ cup fresh orange juice
1 tsp. shallot or yellow onion, minced
1 fresh rosemary sprig, 4" long
¼ (½ stick) cup unsalted butter, very cold
¼ tsp. kosher salt

In a small saucepan, combine the vinegar, orange juice, shallot and rosemary and bring to a boil over medium-high heat. Cook, stirring and scraping the sides of the pan occasionally with a heat-resistant rubber spatula, until the liquid is reduced to 3 Tbsp. (it may be difficult to judge the volume because of the herb sprig in the pan), 3-5 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 blending until almost all of the butter is incorporated, then remove the pan from the heat as you work in the last bit.

Remove and discard the rosemary sprig (squeegee the sauce off it with your fingers so you don't lose a drop) and whisk in the salt. Taste and adjust the seasoning if needed. If the sauce is still very sharp, whisk in another ½-1½ Tbsp. cold butter. For a perfectly smooth sauce, strain it through a fine-mesh sieve. If you're OK with the shallots, serve as is.

If possible, serve right away. To keep longer, transfer to a bowl set over a saucepan of hot water (no hotter than 110°F) or pour into a thermos to keep warm for up to 2 hours.

Makes 2/3 cup (150 mL) glaze.