Grease the surface of a large frying ban with the vegetable oil or butter and then place the pan over medium-high heat. Lay the bacon flat onto the surface of the pan and fry them, flipping every few minutes, until they are crispy but not charred. Remove them and set them aside to cool for 5 minutes. Take 4 of the bacon slices and place them on a separate plate. Cut them into small pieces, about 1 to 1/2 inch around.

Place the ice cream, the milk, the dulce de leche, and the chopped bacon in a blender. Put the lid on the blender, and blend at high speed for about a minute, or until the mixture is thoroughly combined. Pour the milkshake into a clear serving glass and garnish with the single slice of cooked bacon. Serve immediately.