Cut the lettuce heads into quarters, blanch with boiling water, let sit for 2-3 minutes, then drain and squeeze out the water thoroughly. Chop coarsely.
In a saucepan, melt the lard, sprinkle in the flour, and toast it over medium heat, stirring constantly, to a light red.
Add the chopped onion and fry until straw-colored, about 2-3 minutes.
Take off the heat, stir in the paprika, then add the squeezed, chopped lettuce.
Pour in enough water (or bacon cooking liquid, if available - it adds more flavor) to make a thick, spoonable stew.
Cook for a few minutes, season with a little vinegar and salt.
Stir in sour cream before serving and warm through, but don't let it boil again.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.