1 large shallot, finely diced (1/3 cup)
1/2 tsp. chopped fresh thyme
1/2 tsp. finely grated lemon zest
Kosher salt and freshly ground black pepper
Heat 1 Tbs. of the butter in a small saucepan or skillet over medium-low heat until melted. Add the shallot and cook, stirring frequently, until deeply browned, 8 to 10 minutes. Remove from the heat and stir in the thyme. Cool completely.
In a small bowl, combine the shallot mixture with the remaining 2-1/2 Tbs. butter and the lemon zest. Stir to blend well. Lightly season to taste with salt and pepper.
Scrape the butter onto a small piece of plastic wrap, mold into a log shape, and wrap in the plastic. Refrigerate until ready to use. Toss about one-third of the butter (a generous tablespoon) with a batch of vegetables after roasting.