This is a super simplistic setup of an DSMR (P1) energy monitor utilizing the ESP32-C3 (SuperMini) you can get for €1-€2.
The ESP32 is flashed with ESPHome and can easily be integrated into Home Assistant.
It is tested on a DSMR 4. The ESP32-C3 is externally powered by usb since the "slimme meter" couldn't power it.
The update rate is controlled by the meter. It should be possible to use the data request pin, but this would require more parts (optocoupler etc).
Only three parts are used for building