In medium saucepan, melt butter over medium-low heat; sauté mushrooms and onions for about 10 to 12 min or until lightly caramelized. Stir in flour to absorb butter; slowly stir in cream. Increase heat to high, stir in stock and bring to boil. Reduce heat and simmer, stirring occasionally for 20 min or until flavours are blended.
Lightly toast baguette slices in a toaster; set aside.
Place ovenproof soup bowls on baking sheet and ladle soup into bowls. Top each bowl with two baguette slices and sprinkle with Canadian Gruyère and Blue cheese. Broil for about 2 min or until cheese is lightly browned and bubbly.
Place bowls on serving plate and sprinkle with chopped chives. Be sure to warn your guest that the bowl is ultra hot.
Tips: This recipe is perfect for a large crowd because it is easy to double or triple. To make ahead, prepare the soup through Step 1, cool and refrigerate in an airtight container for up to 1 day. Reheat gently until hot and proceed with Steps 2 and 3.