Grease a 24cm dish with plenty of butter or oil. If using cabbage leaves, cut away the inner part of the leaf, as you only need to use the outer 2 inches. Lay them around the rim of the baking dish.
Put the kale leaves into a heatproof bowl. Bring some water to the boil and pour it over the kale to blanch, allowing it to sit for 1 minute before rinsing well under cold water. Squeeze all the water out then chop finely, tossing it into a mixing bowl.
Mix the peas and chopped parsley with the kale, then put this into the prepared baking dish.
Whisk the eggs, basil, cream and seasoning until incorporated, then pour this over the greens in the baking dish.
Lay the asparagus on top, pressing down slightly. Bake in the oven for 1 hour, or until cooked in the middle.
Serve warm or at room temperature with a leafy salad, some beautiful tomatoes and a little pesto to drizzle over the frittata.
Rather than bin the thick stems from the kale, keep them for a soup!