Preheat oven to 375˚F and line a large baking sheet with parchment paper. In a large bowl, toss the broccoli fleurets, the olive oil, and the sea salt and pepper (to taste). Spread the florets in one layer on the prepared baking sheet. Set aside.
In a small bowl, mix the mayo with the mustard. Drop dollops of sauce over the broccoli florets, so that they all benefit from the sauce. Pop in the oven and roast for 15-20 minutes, until the broccoli is tender, but still crisp, and a nice golden char starts to appear on the sauce. Bon appétit!
*You may also use cauliflower for outstanding results.