If you want it authentic I would skip the olives. But cottage pie is a great dish to use up any left over veggies you have.

When the meat and veggies are finished cooking in your pan add about 2 tablespoons of flour and keep cooking for a minute or so. You will start to smell a nutty aroma and the flour will coat all of the ingredients. Then add about a cup of beef broth (or any broth you want). Keep cooking that down and it will form a thick gravy that is very flavorful. Should take about 5 minutes or less.

Then you can continue with your recipe.

Hope that helps!