Heat oven to 400 degrees. If you don't have a convection setting, you may want to do 425.
Slice off the ends of the brussels and then half, lengthwise. I usually let a couple of the most outer leaves fall off to discard, but if any others fall off, you can absolutely use them.
Line a large baking sheet with parchment and add the brussels. Drizzle with the olive oil and salt (add some cracked pepper too). Toss to thoroughly coat and arrange the brussels *flat side down*. This helps them to steam from within and get perfectly tender, while crispy the outside.
Roast for 20 minutes or so, until the outsides are getting crisp and the under side is slightly browned. Don't worry if some of the leaves are getting brown / crispy, that's the good stuff!
While they're cooking, make the maple dijon mix. Then drizzle all over and toss to coat. Don't worry about rearranging them flat side down. At this point, they can fall however they want (as long as they're not too overly crowded on top of each other).
Roast for another 8-10 minutes, or longer if you like them even more done. Taste to see if they need any more salt or pepper.
Enjoy right away or reheat on the stove to crisp up again at a later time!