Set a medium sauce pan to medium heat. Add your butter and let it melt for a minute. Then add the cornstarch and whisk to avoid lumps. Add milk and stir it in until evenly combined. Add your beef stock and stir it in as well. Reduce the heat to low and simmer until thickened, about 5 minutes. Season with salt and pepper. Then move the gravy to a thermos to keep warm.
Heat a large skillet or a flat top to medium high heat and coat with olive oil. Add the sausages and sear all sides, for 1 to 2 minutes per side. Add a little bit of water and cover with a cloche to cook the sausages all the way through, for about 8 minutes. Remove from the heat and set aside to rest for a few minutes before slicing into bite sized slices.
Cook the fries in the oven according to the package instructions or until golden-brown.
Build the poutine by spreading the french fries out on a plate and season with a pinch of kosher salt. Pour on the gravy and top the fries with your cheddar and bacon sausage, cheese curds and green onions.