As soon as the asparagus comes out of the oven, transfer it to a warm serving platter or a white plate. Immediately drizzle the melted butter evenly over the hot spears so it sinks into the blistered spots and coats the crispy tips.
Finish with a small pinch more coarse sea salt over the top for texture. Serve right away while the asparagus is still hot, glistening, and crisp at the edges.
For a lemony twist that stays low carb, add very finely grated lemon zest (no juice, to keep the ingredient list conceptually tight) over the asparagus along with the final sprinkle of sea salt. If you want a slightly richer flavor, use all butter instead of part olive oil, but keep the oven temperature the same and watch closely so the milk solids on the pan don’t burn. You can also play with texture by roasting the asparagus a minute or two longer for extra-charred tips, especially if your spears are thick. To make this ahead for company, trim and dry the asparagus earlier in the day, then oil and salt just before roasting so it doesn’t soften. If you have a convection setting, use it and check early—convection promotes even browning and can shave off a minute or two of cooking time. Finally, for a subtle nutty edge without adding ingredients, preheat the empty sheet pan in the oven while it heats; adding the oiled asparagus to a hot pan helps blister the stalks and keeps them beautifully crisp.