To prepare the frittata: For best results, use a 24cm cast iron pan. It holds heat well. It helps cook the frittata evenly. It also gives a golden, lightly crisp edge.
Heat a little oil in the pan over a medium heat. Add the sausages and cook for 4–5 minutes. Remove from the pan and set aside.
Add a little more oil to the frying pan, then add the mushrooms and fry for 1-2 minutes. Then add the chopped tomatoes, scallions and spinach leaves and cook until the spinach wilts.
Meanwhile, whisk the eggs in a large bowl, add the cream and feta and season. Then add the sausages and vegetable mixture from the frying pan. Stir well to combine.
To cook the frittata: Heat a little more oil in the frying pan and add the egg mixture. Move the pan around to let the egg mixture run under the vegetables and sausages and reach the bottom of the pan.
Turn the heat to low, then cook for about 12 minutes until nearly set.
Preheat the grill to medium. Place the frying pan under the grill and cook for about 10-12 more minutes, until the top is set and golden.
To serve: Allow to sit for about 5 minutes before removing from the pan and slicing into wedges. Serve with a green salad.