Portobello-stuffed Swiss Chard Leaves

Wash chard.
Cut stems from leaves.
If stems or ribs are stringy, cut the bottom and pull strings away. Dice stems very fine.
In a pot of boiling salted water, blanch leaves for 1 minute.
Immerse immediately in a bowl of ice water, drain and set aside.
In a skillet over medium heat, cook shallot and garlic in hot oil for 1 - 2 minutes.
Add mushrooms, increase heat and cook 3 - 4 minutes. Set aside.
Preheat oven to 350°F (180°C).
In a pot over medium-low heat, cook stems with balsamic vinegar until liquid is evaporated.
In a bowl, combine cooked stems with rice and mushroom mixture. Stir in nuts and seasonings.
In the centre of each leaf, spoon some stuffing.
Fold sides over and roll up leaf.
Transfer stuffed leaves to a lightly greased baking dish with chicken stock in the bottom.
Cover and bake 15 - 20 minutes.