Yes you can, but you have to melt the blocks of solid fat slowly in a normal pan first and then pour the melted fat carefully into the fryer before switching the fryer on. It is possible to let the fat solidify in the fryer. If you do, do not forget to punch a few holes in the fat with a fork before switching the fryer on again to prevent the fat from spattering. Be careful not to damage the heating element when doing so. Philips advises to use liquid fat or oil as those are better for your health.