How to link HA and Alexa without using the cloud as I am already an Alexa Endpoint

I was wondering if anyone has tried integrating Alexa and HA without using the Nabu Casa cloud. I already have an Alexa Endpoint at my house as I have custom integration built to control loads of integrations using voice. So I am all set up with domains / certificates etc and I have apache running the app that communicates with Alexa. I am familiar with developing Alexa skills etc.
So the question is has anyone attempted to (and is it even possible) to setup Voice control of HA tasks without using the Nabu Casa cloud.

Happy to read anything - but I can’t find anything from googling :grinning: