Mash the camembert and soft butter together with a fork until well combined, then knead in the paprika powder, salt, pepper, beer, and egg yolk until smooth. (Alternatively, finely dice half the onion and knead it into the mixture along with the other ingredients if you prefer onion mixed throughout rather than on top.)
Use a teaspoon dipped in water to scoop portions onto a serving plate.
Cut the onion into rings and arrange on top of each portion, then sprinkle lightly with paprika.
Serve with pretzels, bread, and a cold beer on the side.