In a small skillet, melt the butter and add the flour.
Mix and cook the roux for about 2 minutes. Remove from the heat and set aside for later.
In a large pot, boil the potatoes until they are soft and ready to be mashed.
Drain the potatoes and place them in a stand mixer and whip them until somewhat smooth, do not overwhip them otherwise they become very gluey.
Add the milk, butter, salt and pepper and continue to mix until fully incorporated.
In a large non-stick skillet, cook the onions in olive oil for 5 minutes or until onions become soft and tender.
Add the sausage, boudin and the beef stock to the skillet of cooked onions and continue to cook on high heat for 5-7 minutes.
Remove the sausage and boudin and set aside.
Add the roux to the liquid and continue to cook for 5 minutes while stirring constantly.
Add all the remaining ingredients and continue to cook on low heat while stirring constantly.
Once the dish is thick but still somewhat saucy, kind of like a melted cheese sauce, then remove from the heat.
Place a healthy portion of the mashed potatoes on a plate then place a section of sausage and a section of boudin on top of the mash. Spoon the onion gravy on top generously. Garnish with fresh chopped green onion.