In the Aragon region of Spain, where I lived for ten years, borage (
borraja) is a popular winter vegetable. They harvest the stalks when they are about 30-40 cm long (12-15 inches), and chop and boil with potatoes. Serve like that with a sprinkling of olive oil and some bread on the side. Some people laboriously scrape the bristles off the stalks but, if the stalks are young, the bristles are perfectly edible once cooked.
Below is a link to a short video of a popular Spanish TV chef doing a more elaborate recipe in which he boils the stalks separately (removes leaves first but doesn't bother removing bristles), fries potatoes separately in chunks, then sautés garlic, adds chunks of Spanish cured ham (optional for vegetarians
and then a few spoons of flour, plus some of the borage cooking water to make a sauce. Finally, cooked borage and fried potatoes on top.
The video is very clear even if you don't speak Spanish. In particular, it shows clearly what the stalks should look like for cooking.
https://www.youtube.com/watch?v=io8MF1Zov9s
In northern Spain, it's a winter crop, so I understand it's planted in the autumn. The only time I tried to grow it, I planted it in the spring, and it bolted before I had a chance to eat any!