Begin by heating the butter and olive oil In a over medium-low heat.
Once the oil is hot and butter is bubbling, add the onions, carrots, and celery, and sauté the veggies until the onions are turning translucent and veggies are beginning to soften.
Next, add the garlic and continue to sauté for another 2 minutes.
Add the ground lamb or beef and cook the meat until fully browned, stirring occasionally.
As soon as the meat has fully cooked, add the tomato paste, parsley, rosemary, thyme, salt, pepper, frozen veggies and flour. Stir everything to combine thoroughly. Reduce the heat to low and pour in the Worcestershire Sauce, Beef Stock, and Guinness Stout. Stir the mixture constantly until it's fully thickened, and remove the skillet from the heat.
Preheat the oven to 400°f.
Turn the oven to broil for about 2 minutes to get the top extra browned and colorful.
Remove the from the oven, serve, and enjoy!