Toss broccolini with olive oil and kosher salt, then spread in a single layer on a sheet pan.
Optional: grate parmesan over the top before roasting.
Roast for 20 minutes, flipping halfway through, until stems are tender and tops are crispy and golden.
Make the Miso Bagna Cauda
In a small bowl, whisk together red miso, lemon zest, and lemon juice.
Slowly whisk in the olive oil to emulsify.
Stir in garlic, onion, parsley, and season with salt to taste.
Finish and Serve
Remove broccolini from the oven, transfer to a platter, and spoon the miso bagna cauda over the top. Serve immediately.
Notes
Storage: the miso bagna cauda keeps in an airtight jar in the fridge for about a week, whisk it back together before using. Broccolini reheats fine in a hot oven for a few minutes, just add the sauce after.