It is some brassica but I don't think they are brussels sprouts. Brussels sprouts would be small cabbages along the stem and my stems are a lot thicker. Eventually the cabages including Brussel sprouts will go to seed and your plant is definitely blooming.
Are you sure? To me this looks like a lettuce -- Bibb type or maybe Romaine -- gone to seed....
-- if the seedheads sprout fluffy pompoms like miniature dandelions they are definitely lettuce. Mustard/cabbage family seeds grow in long skinny pods.
