In large bowl, combine all ingredients except grated potatoes and grated carrots. Mixture will dry and crumbly.
Give grated potatoes a slight squeeze to remove a bit of moisture (they will still be quite wet). Add squeezed potatoes to mixture. Add carrots. Mix thoroughly. From the moisture of the potatoes, it will start looking a bit more like a cake.
Put large stock pot on stove, with steaming rack in bottom. Put three inches of water in bottom of stock pot.
Thoroughly spray inside of #3 can with non-stick spray. Pack entire mixture into can, and pack down lightly (not too much.) Make sure there is at least two inches of clearance to the top of the can. Cover with aluminum foil.
Place aluminum foil covered can on top of rack in stock pot. Cover with lid, and turn on stove to medium high. Steam pudding for 3 hours, checking water level on occasion.
After 3 hours, remove aluminum foil and touch pudding. It should feel bouncy and fully-cooked. Allow to cool for a few minutes, then invert onto plate. Pudding should slide right out. While pudding cools, make toffee sauce.