Place 1 cauldron
Place a pointed dripstone directly below a block
Place a lava source block above the pointed dripstone
Wait for the cauldron to fill with lava
Use a bucket to collect lava from the cauldron
Repeat the setup with multiple cauldrons for more lava
If you want a renewable lava source, keep the lava block and dripstone in place
If you want an infinite lava farm, automate bucket collection and refill as needed