I finish my cutting boards first with pure mineral oil, I buy the stuff from the pharmacy aisle of the grocery store they sell as a laxative. I sand to 220 grit, wipe with a wet (with water) rag to raise the grain, sand it again at 220 grit, and then flood the surface with oil and massage it in. I often feel it soaking in under my fingers. I let it sit for about an hour, then flood again any dry spots.

Then I’ll rub it with “board butter” aka food safe paste wax aka mixture of mineral oil and beeswax. Rub it in, let it dry for a few minutes, buff it off. Let that sit for a few hours and the board is ready to use. As you wash the cutting board, this finish will wear off, and every now and again you have to reapply the wax.