Pat dry the bison and season with salt and freshly ground black pepper.
Heat an enamel coated, cast iron Dutch oven over medium high heat.
Add just enough vegetable oil to coat the bottom of the pot.
Once the oil is hot, add the bison to the pan.
Let it sit and don’t turn it until it is deep golden brown in color.
Then flip and brown on the other side.
Remove the bison from the pan and set on a plate.
Add the green onions, garlic, lemongrass, and ginger to the oil.
Stir until they are just starting to brown.
Add the Madeira, soy sauce, rice wine vinegar, brown sugar, star anise and water.
Add the bison to the pot.
Bring to a simmer, then lower heat and cook for 3 hours at your stove top’s lowest setting.
After it is done cooking, remove the bison from pot, remove any silver skin from bison.
Alternately you could place in a crock pot to finish.
Put the bison in a heat proof dish and cover with aluminum foil and keep it warm in the oven.
Put the pot over medium heat and cook until the liquid has reduced by half.
Yams: In a medium pot, add the yams and ginger and cover with water.
Cook for about 20 minutes, or until tender.
Remove the yams from the water and, using a ricer, press the yams into a medium bowl. Next, whisk with the heavy cream, olive oil and then season with salt and white pepper to taste.
To serve: spread the whipped yams on a plate or in a bowl, top with the bison and spoon the sauce over the top.
Garnish with green onion.