Regarding covering food up [to keep it warm on Shabbat]. Is there a hint of a transgression in our contemporary stoves, whereby we cover up the pot and sprinkle ash on top of the coals? Also regarding those who bury the pot in the ground, and bury hot coals around the pot, is all this permitted or not?¹

footnotes: ¹ See Tosafot on Shabbat 48a:1, which starts by questioning the practice of burying food, even when the coals are covered with ash. The Ri then gives a reason for allowing contemporary buried ovens (called אשטר"א, l'âtre or l'aistre) that have space built in between the walls and the coals. This practice and reasoning is repeated by the Rosh on Shabbat 4:2.

They responded: We have already indicated to you the chosen authority¹, "And you shall act in accordance with the instructions given to you," (Deuteronomy 17:11) "For he is an angel of God of Hosts, and rulings are sought from his mouth." (Malachi 2:7)

footnotes: ¹ Possibly referring to R. Isaac Alfasi (cf. Siman 2). However, the text of Rif Shabbat 22a is ambiguous on this point in question