What is the association to omelets? We have "pie in the sky" to refer to someone's dream vision of a goal or object-as in something without restrictions.
I think that, maybe, years ago, population was very poor so dream about eating an omelette it would be impossible. This idiom is from Catalonia and is written in catalan.
Hi Judit! Your idiom is very interesting because of that omelette! :) We have same kind of idiom in Finland: " Taivaanrannanmaalari". It means that some person is painting to the sky. Typically "taivaanrannanmaalari"-person sounds not like a realist and his thinkings so positive that they sound like a dream.
When I was a kid some adults said to me that I was and omelette dreamer because I was always imagining no real things and playing fantastic games.