External rendering of Razor (e.g. for newsletters)

var p = (WebPage) WebPageBase.CreateInstanceFromVirtualPath("~/Templates/Newsletter.cshtml");
var ctx = new WebPageContext(new HttpContextWrapper(context), p, null);
var htmlWriter = new StringWriter();
ctx.PageData["NodeOrWhatever"] = nodeOrWhatever;
p.ExecutePageHierarchy(ctx, htmlWriter);

var html = htmlWriter.ToString();