Melt butter with the olive oil in a large skillet over medium heat, and cook the onion just until it begins to brown, about 8 minutes; stir in the potatoes and carrot, and cook until tender, about 15 minutes, stirring occasionally. Stir in the cubed corned beef, parsley, thyme, salt, and pepper. Let the mixture cook until hash is crisp and browned, stirring often, 10 to 15 more minutes.
