Posh Bubble & Squeak - Deliciously Yorkshire

Ingredients

• 6 tablespoons unsalted butter, or vegetable oil
• 1/2 cup finely chopped onion
• 1 pound mashed potatoes, about 2 cups
• 1 cup leftover vegetables (cabbage, kale, peas, cooked swede, cooked carrots, and/or cooked Brussel sprouts), finely chopped
• Bacon, leftover roast, bangers, and/or ham, chopped, optional
• Salt, to taste
• Freshly ground black pepper, to taste