.NET Core is a free and open-source managed software framework for Windows, macOS, and Linux. It consists of CoreCLR, a complete runtime implementation of CLR, the virtual machine that manages the execution of .NET programs. CoreCLR comes with an improved just-in-time compiler, called RyuJIT.
For example, Microsoft's Bing search engine now runs on an open-source platform - .NET Core 2.1, to be precise.
A number of improvements to .NET Core account for most of the performance gain, including vectorization of string equality and string.IndexOf/LastIndexOf using the new Span<T> type, which speeds up HTML rendering and manipulation; devirtualization for EqualityComparer.Default, which improves dictionary performance; write watch for concurrent GC, which brought a reduction in CPU usage; and others.
Setting up a project from an empty template is always a preferred approach and it is simple and quick to set up a web application using ASP.NET Core.