Place a large saucepan over high heat.

Add the olive oil, garlic, oregano, onion, and celery and saute for 5 minutes, until the onion is starting to become translucent.

Add the salt and ground beef, stirring continuously to break apart the meat while it browns.

When the beef is browned add the tomato paste and stir well.

Add the beef stock and simmer uncovered for 20 minutes until the liquid has reduced.

Add the thyme and frozen mix and simmer for 5 minutes before removing.

Spoon the beef mixture into your casserole dish and set aside.

Preheat your oven to 175°C.

Fill a large saucepan two-thirds full of water and bring to the boil.

Add the cauliflower florets and cook for 7-10 minutes until tender.

Carefully pour the water and cauliflower florets into a colander and drain well.

Return the drained cauliflower to the saucepan, along with the butter, salt and pepper.

Using your stick blender, blend the cauliflower into a smooth mash.

Add the egg yolks and blend well, add the grated cheddar and mix.

Gently spoon the mashed cauliflower onto the beef mixture into your casserole dish.

Bake the pie in the oven for 25-30 minutes, until the mash is golden brown.