One cord per cabinet is best.
When you plug one into the 8 ohm jack, it's connected to the 8 ohm tap on the output transformer. The 4 ohm jack is similarly connected to the 4 ohm tap. Use that if you're plugging in a 4 ohm cabinet. However, when you plug into the 4 ohm jack, it places the 8 ohm jack in parallel, disconnecting it from the 8 ohm tap and connecting it to the 4 ohm tap. So, plugging one cord into each jack connects both cabinets to the 4 ohm tap. Since two 8 ohm cabinets in parallel come out to 4 ohms, this is exactly right. If you daisy chain, run from the 4 ohm jack to one cabinet, then from the first to the other cabinet. Two cords from the amp is better, though.