This depends on a lot of things, mostly how many recipes you plan on having and if you want to be able to search, sort, or style the recipes.
Text files are the simplest way. You could add some simple search and ordering functionality.
If it's in this hundreds, you could get by with using xml and a serializer. It would allow you to later style the recipes and it gives the data some structure. If your recipes enter the thousands, this way may become a nightmare.
The best way would be a database. Sql Server Compact is a free option that links up nicely with c# through something like Entity Framework. This option will take the longest by far if you're not already familiar with databases or ado.net or entity framework.
