Preheat the oven to 375 degrees and prepare two baking sheets with foil or use nonstick baking sheets. Thoroughly rinse produce and pat dry. Mince garlic. Cut onion into a fine dice. Remove gills and stem from mushroom cap with a spoon. Scrub fingerling potatoes and halve large ones, leaving smaller ones whole. Stem oregano.

In a small bowl, add 1 clove of minced garlic, balsamic vinegar, 1 Tbsp. oregano (reserving rest for garnish), 1 Tbsp. olive oil, and salt and pepper to taste. Whisk together then add Portobello caps to mixture, covering completely. Marinate caps for 10 minutes.

In a mixing bowl, add 1 tsp. olive oil, 1/2 tsp. salt, and 1/4 tsp. pepper. Add potatoes and toss, ensuring they’re completely coated. Arrange potatoes evenly and without overlap on a prepared baking sheet, putting halved potatoes flat-side down. Bake in oven 35 minutes, moving potatoes every so often to ensure even cooking. Potatoes should be browned and somewhat crispy. Lower oven heat to 325 degrees to keep warm before serving. The vibrant purple color sometimes cooks away during roasting, so feel free to roast and then cut the potatoes to reveal their gorgeous jewel-toned insides.

As potatoes roast, start the sauce. Heat 1 tsp. olive oil in a medium pan over medium heat. In a small bowl, whisk together bouillon cube with 1 1/2 cup warm water until dissolved. Add remaining garlic and onion to pan and cook until translucent, about 4 minutes. Sprinkle with flour and stir to coat. Add bouillon liquid, tomato sauce, white vinegar, paprika, and red-pepper flakes to taste. Bring to a boil, reduce to a simmer, and let cook until slightly thickened and aromatic, about 30 minutes. Before serving, stir in any of the juices from the portbello roasting. Salt and pepper to taste. Set aside and keep warm.

About 1/3 of the way through cooking potatoes and sauce, prepare to bake mushrooms. Arrange marinated caps in a prepared baking dish and place in the oven (at the same temperature as the potatoes) to cook 15-20 minutes or until tender and the juices have released. Remove from oven, allow to cool, and reserve any juices for the sauce.

Arrange a serving of crispy fingerling potatoes on the plate. Add Portobello mushroom cap on top of potatoes. Drizzle a generous serving of tomato sauce. Garnish with fresh oregano and freshly cracked black pepper.