ASP.Net Core gotcha: Hosting my site in IIS Express, not Kestrel

I did something and suddenly my API was not run in IIS Express anymore, but in Kestrel. I reviewed code changes, configuration changes, all to now avail. I don't want Kestrel, I want IIS Express!!! Why did Visual Studio suddenly decided to switch the development server?

Solution: it is your Visual Studio. The button you use to start debugging has a little dropdown that allows you to choose which server to use. I had probably pressed the wrong one at some point.