Start by preparing the ingredients. In order to finely cube the sweet potato, I square off the sides, peel off any additional skin, then julienne, followed by slicing into small cubes (around 3mm squared or so).
Dice the red onion, finely slice the red chilli, garlic, slice the spring onions, then set aside.
Crack the eggs into a small mixing bowl, add the Dijon mustard, parsley, salt and black pepper, and beat gently with a whisk, then set aside.
Bring a medium-sized non-stick frying pad to a medium high heat, add the olive oil then drop in the knob of butter. Once melted, add the cubes of sweet potato and soften for 3-4 mins. Turn over the cubes, then add the red onion, garlic, and red chilli and continue to sweat and stir gently for a further 3-4 minutes.
Next, add the spring onion, mix thoroughly, and continue to to cook for another minute or two.
Meanwhile, bring the grill to a medium heat.
Pour the seasoned beaten egg / Dijon mustard mix into the pan, and gently swirl around to ensure that everything is evenly covered and as level as possible. Continue to cook until the bulk of the Tortilla starts to become firm. Give the pan a very gently shake from side to side, and the tortilla should start to loosen from the base of the pan (aided by being non-stick, naturally!).
Using a vegetable peeler, shave off a few slices of Parmesan cheese and add evenly place on top of the Tortilla.
Remove pan from heat and place under pre-heated grill for 3-4 minutes, or until brown.
When serving, I like to offer a portion of both sides for the Tortilla, and include a side salad.