Q.Romanesco broccoli
I had a beautiful plant but absolutely no head formation.

You are in zone 5a, so I would assume you are growing in a greenhouse or possibly a cold frame.
Romanesco is not truly Broccoli and not truly Cauliflower.
It is very temperamental to temperature and needs consistent water and highly organic soil to thrive.
It requires a slightly shaded location with alkaline soil and plenty of room to spread it's roots to spread.
Northern regions should plant in spring right after danger of frost has passed.
https://www.gardeningknowhow.com/edible/vegetables/broccoli/broccoli-not-forming-heads.htm
https://www.gardeningknowhow.com/edible/vegetables/broccoli/growing-romanesco-broccoli.htm