I have a question about the recipe "Harvest Chicken Pot Pie" from adamnsvetcooking. I'm loosely following the recipe (no mushrooms in the house, e.g.). THe filling is very thin -- I used the 2 cups stock and 1 tbsp flour like the recipe, and it's been simmering to try to thicken for over a half hour now. How can I get this to thicken? It's still soup-like. What should I do?