Melt the butter in a large, deep skillet. Cook until the butter is browned, about 8-10 minutes.
Add the onions and parsnips and cook over low heat until they begin to soften and brown lightly, 10-12 minutes. Toss frequently to prevent burning (especially the already browned butter).
Add the sliced garlic and continue to cook until the vegetables darken a little more, 3-5 minutes.
Stir in the brown sugar, salt, and pepper until well combined. Add the wine and cider and bring the mixture to a simmer. Simmer, tossing occasionally, until the liquid is almost entirely reduced (it will make a thick glaze over the vegetables), 12-15 minutes.
I always carry three kinds of hot sauce in my purse. I have a soft spot for making people their favorite dessert, especially if it's pie. My first cookbook, The Fearless Baker, is out on October 24, 2017.