Preheat oven to 400 degrees F.
In an 8 inch oven safe skillet, melt butter or ghee on medium high.
add garlic, onions, mushrooms and Italian sausage andcook until the onions are translucent
In a medium mixing bowl, beat the eggs
Add the seasonings and mix well
Turn down stovetop heat to medium.
Add egg mixture to skillet.
Gently stir, incorporating the vegetables into the eggs.
After a few minutes and once the eggs begin to cook around the edges, top the egg mixture with the sliced tomato and put the skillet into the oven.
Cook for 20-25 minutes.
Remove skillet from oven and allow the frittata to set for at least 10 minutes.