Common salt, NaCl is an ionic compound completely soluble in water but insoluble in organic solvents like Dichloro methane or DCM. Butter is a covalent organic compound which is insoluble in water but soluble in organic solvent like `CH_2 Cl_2` or DCM.
The two components salt and butter can be separated on the basis of their solubility difference. Add some DCM to the mixture and filter. DCM dissolves water leaving solid NaCl intact, which is collected as residue in the filter paper. Wash the residue with two small portions of fresh DCM and combine the collected filtrate. Take the combined filtrate on an evaporating dish and drive off the solvent by gentle heating. This would recover the total amount of butter present in the mixture. The salt can simply be scraped off from the filter paper.