Beets and Caramelized Onions with Feta
2 TBSP. Apple Cider Vinegar 1 Tsp. Dijon Mustard (Preferably Whole-Grain Or Coarse-Grain) 1/4 Tsp. Black Pepper 3/4 Tsp. Salt 5 TBSP. Olive Oil 1 lb. Onions (2 Medium), Quartered Lengthwise, Then Cut Crosswise Into 1-Inch Pieces 2 (15 oz.)…