The answer is villi.
The main function for villi is to speed up the absorption of digested food molecules in the small intestine, as the villi can provide a larger surface area for the small intestine.
In addition, on each villi, there's also smaller micro-villi. Same purpose, to increase the surface area.
Food molecules are absorbed by the process of diffusion or active transport, and the rich blood supply of villi can surely speed that up as it can always remain a steep concentration gradient thus increase the rate of molecules transfer.
