• Peel and cube potatoes, then place potatoes in a large saucepan and fill with water until potatoes are completely covered by an inch.
• Bring to a boil, then reduce heat and cook for 15-20 minutes, covered, until potatoes are tender.
• Reserve 1/2 cup cooking liquid; discard remaining liquid.
• Mash the potatoes with a potato masher, making sure to get rid of as many lumps as possible, but not over mixing. And set aside.
• Get your kitchen thermometer out, and add your milk to your reserved liquid, adding until temperature reaches 110° (Note 1)
• Pour liquid into the bowl of a stand mixer, and add your yeast. Dissolve yeast
• Add the remainder of the milk to the mashed potatoes to help cool them. Use your kitchen thermometer to check the temp, and when it reaches 110 °, add the mashed potatoes, milk, 1/2 cup of canola oil, sugar, eggs and salt to the yeast mixture in your stand mixer bowl.
• Using a stand mixer fitted with the dough hook, mix flour into the dough, a cup at a time to form a soft dough.
• (Note 2)
• Once mixed, place dough in a bowl greased with cooking spray or oil, turning once so the whole dough has a light coating of the oil. Then cover with plastic wrap. Place a dish towel over the plastic.
• Let dough rise in a warm place until doubled, about 1 hour.
• Punch dough down, then let the dough rise again until doubled, about 20 minutes.
• Flour a work surface, and using your hands, tip dough out, and form a round of dough that is about 10 inches in diameter, and 1 1/2 inches thick.
• Cut with a floured 3 -4 inch donut cutter. You should get roughly 12 large doughnuts (Note 3)
• Put 6 cups of oil into a heavy bottomed pot or dutch oven, and heat to 350° F. Use a liquid/candy thermometer to check temp, and keep it at 350° F. (Note 4)
• Fry donuts, two at a time, until dark golden brown, about 4 minutes per batch, rotating the donuts half way through. Do not allow the heat to exceed 350° F, the outside will cook too fast and leave the inside doughy. (Note 5)

Glaze

• In a large bowl, combine the confectioners' sugar, milk, heavy cream and vanilla until smooth.

Chocolate Sauce

• Stir brown sugar and cocoa powder together in a small bowl, and set aside.
• In a small sauce pan, over medium-high heat, add unsalted butter and heavy whipping cream together, and bring to a soft boil.
• Let boil for 2-3 minutes, stirring occasionally.
• Stir in brown sugar and cocoa powder mixture and whisk until smooth.
• Remove from heat, add vanilla and salt.
• Whisk, and let sit a minute to thicken.

Assembly

• Dip warm donuts in glaze.
• Place glazed donuts on a wire rack with parchment under it, excess glaze will drip off, and they will cool on wire racks.
• Spoon chocolate sauce over hot glazed, donuts, sprinkle with sprinkles (if desired) while still wet/hot, and let glazes set up while donut cools.