Preheat your oven to 180c fan-forced.
Bring a medium sized pot of water to the boil and add in kipfler potatoes. Boil till just tender, drain then set aside. When the potatoes are cooled enough sliced them into 1/2 cm rounds.
In the interim prepare the silverbeet by removing the hard stalks and roughly chopping up. Add the silverbeet to a medium heat frying pan with some extra virgin olive oil and sauté till nicely wilted. In the last few minutes and in the crushed garlic and stir through. Set aside.
Add to a medium sized bowl the eggs, milk, nutritional yeast, salt, pepper and mayonnaise and whisk well.
Take a deep-dish baking pan and start by placing a layer of the sliced potatoes using around one third of them. Top with some of the spring onions and then 1/2 of the wilted greens. Repeat the potato layer again followed by the spring onions and the greens. Finish with the remaining potatoes and any left over spring onions.
Pour over the egg mixture making sure it is evenly distributed throughout the frittata. Now top with the truss tomatoes still attached to the vine. Drizzle with a little olive oil and season with some more pepper then place in the oven for 60 - 65 minutes till cooked through in the centre. The frittata is done when you press on the centre and no egg oozes out.
Serve the frittata warm or cold as is or with a fresh green salad.