From Wiktionary, the free dictionary
Literally, “to roast butter in a spit”.
assar la manteiga ne l speto
- to carry out a very difficult or impossible task
- “assar la manteiga ne l speto” in Amadeu Ferreira, José Pedro Cardona Ferreira, Dicionário Mirandês-Português, 1st edition, 2004. [1]