Snaps are tender, crisp, undeveloped black-eyed pea pods snapped off the plant before the peas inside are formed.
Heat oven to 400 degrees. Cook garlic in aluminum foil about 25 minutes, until cloves are soft. Remove from heat. When cool enough to handle, scrape soft garlic from cloves.
If using snaps, cook them in salted boiling water just until tender, 1 to 3 minutes. Transfer to a bowl filled with ice water to stop the cooking, drain, and cut into 1-inch lengths. Set aside.
Heat oil in a small skillet. Add garlic and shallot; cook over medium heat until minced shallot is translucent, stirring and smashing the garlic with the back of a wooden spoon.
Stir in the wine and vinegar; cook until reduced to 2 tablespoons, about 2 minutes. Remove from heat; whisk in the butter, a piece at a time, until fully incorporated. Season with salt and pepper. Stir in parsley just before serving. Place hot black-eyed peas, and snaps if using, in a serving bowl. Top with warm sauce; serve.