In a large bowl place, the sliced Brussels sprouts and drizzle them with olive oil. Mix well and transfer them, cut side down on a cookie sheet.
Bake in the preheated oven for 20 minutes. They need to be brown and soft.
Meanwhile, whisk together mustard and mayonnaise. When the sprouts are done, mix them with the mustard mayo mixture.
Season with salt and pepper and add the parsley. Give it a last toss and serve.
Notes
Do not overcrowd the baking sheet, or they will produce steam when they roast and will never crisp up to your liking.If making them for a crowd, use two baking sheets. You will thank me for it later.
Giangi's Kitchen provides nutritional information, but these figures should be considered estimates, as a registered dietician does not calculate them.