Finely crush breadcrumbs, either in a blender (easiest method) or by placing them in a bag and crushing with a rolling pin or heavy object.
Preheat oven to 425 F.
Cut cauliflower into florets.
Whisk milk, cornmeal, and oil, then toss with the cauliflower in a large ziploc.
Put the cauliflower in a colander to drain off excess batter.
Toss with the breadcrumbs.
Arrange in one layer on a parchment-lined baking sheet.
Bake 35-40 minutes.
Meanwhile, make the lemon sauce by whisking together all remaining ingredients except cornstarch.
Then quickly whisk in cornstarch.
Turn heat to medium.
Stir frequently – it thickens pretty quickly.
Remove cauliflower from oven and stir into the sauce.
