Separate florets of broccoli and cauliflower and boil for 10 minutes. Drain and let cool.
Using a mandoline, slice potatoes thinly then cover the base of four 8 inch round tins with the sliced potatoes. Drizzle oil over the potatoes and cook in the oven at 180 C / Gas 4 for 10 minutes or until edges of the potato start to brown slightly.
Fry the onions in the remaining oil and the butter till softened. Remove from heat.
In a bowl, mix together the eggs with the tarragon, Italian herbs, paprika, soy sauce, peas, sweetcorn and cheese. Add the broccoli, cauliflower and onion. Season with salt and pepper.
Pour the egg mixture over the potatoes in the trays. Place the bacon on a separate tray.
Place all trays in the oven and bake for 30 to 40 minutes.
Remove from oven and chop the bacon once cool enough to handle. Sprikle on top of the frittatas, then drizzle mayonnaise over top.