Ingredients For This Step: 4 tablespoons unsalted butter, 3 cups Pearl Onions (Small Diced), 1 cup Leeks (White Part Only And Small Diced), 2 Sweet Potatoes (Peeled And Cubed Into 1" Pieces), 1 Clove Garlic (Minced), And 1 tablespoon Picked Thyme Leaves. For The Pot Pie: To the same pan, add the 4 Tablespoons of butter along with the onions, leeks, celery, sweet potatoes, garlic, and thyme leaves. Add a large pinch of salt and sweat the vegetables for about 5 minutes.