Miui Pie Firmware

[aziz30]

Hello,

I wanna try an AOSP rom based on pie firmware. Now I'm on Oreo Firmware.
What's the correct procedure to flash an AOSP rom based on Pie firmware ?

Should I flash :

-Pie firmware then
-Aosp rom pie firmware

What about TWRP ? Is there any TWRP Pie firmware ?

Thanks for your answers.