CardRenderService.cs

//the underlying CardRenderService
public class CardRenderService
{
    private RazorLightEngine Engine;

    public CardRenderService()
    {
        Engine = new RazorLightEngineBuilder().UseMemoryCachingProvider().Build();
    }

    public async Task<string> RenderCard(string key, string input, object data)
    {
        return await Engine.CompileRenderAsync(key, input, data);
    }

}