I don’t understand cooking levels. I can see in local chat that my cooking level has gone up to 79. But I can’t buy recipes that require level 30. When I look at my professions tab is says Cataclysm Cooking 1 of 75. I don’t understand. How can I have level 79 but only show 1 out of 75. Can someone explain this to me, please?
Professions are divided up by expansion, and each one levels individually. (This was a change made in BfA, so older guides will have the wrong info on professions levels.) It gets confusing because the main city trainers teach both “Vanilla” and Cataclysm professions, and they are just jumbled together in the training window.
When you are looking at the cooking window, the top level dividers are the expansions. (Vanilla cooking is listed as “Old World Recipes.”) They’ll have a progress bar next to the section divider text you can hover over to show your progress for that expansion. (The main profession screen will show your level for the highest expansion you have at least 1 skill in.)
If your cooking skill is at 79, this is probably referring to “Old World Cooking,” which I believe levels up to 300. Cooking for other expansions topped out at 75, I believe, most of the time. Later expansions might go higher.
If I recall correctly, you need a special currency to buy Cataclysm recipes 
[Epicurean’s Award]. This might be why you can’t buy the recipe even though you have high enough skill to cook it. Under normal circumstances, you can buy a recipe or get it as a random drop even if you aren’t high enough skill to use it.
This guide might be helpful for Old World Cooking
and Cataclysm cooking: