I haven't done much historic cookery lately, because it's been very hot here. I suspect that, in Viking times, people would have simply eaten bread and cheese on a hot day, but my husband won't eat cheese. But he will eat chicken salad, a much more recently invented dish, so I've been playing with chicken salad recipes again.
Our current favorite recipe is from About.com's Southern Food site, where I found a simple, spicy recipe called "Cajun Chicken Salad with Pecans." The novel ingredients in this concoction are finely chopped pecans and a quarter-teaspoon of Tabasco sauce. My husband, who is inordinately fond of hot sauce in general and Tabasco in particular, raved about the results.
When it was time to make up a second batch, he wanted to replace the green onions in the recipe with leeks. Now leeks are about as un-Cajun as you can get, being an old world plant that likely did feature in Viking era cuisine, if not necessarily in Scandinavia.
On the other hand, leeks have a mild oniony flavor that's not all that different from green onions, so I figured the substitution would work just fine. We tried it last night, and the result's just as good as the original recipe. I bet that any mild onion would work--maybe I'll track down some Vidalias for the purpose.
All of this just goes to show how wonderful it is to be able to visit your area supermarket, collect ingredients from two different continents and whip up an interesting multicultural experiment for dinner.