To a medium saucepan, add the ale, thyme, and bay leaf. Bring to a boil then reduce heat to low, simmer for 5 minutes or so or until the liquid reduces to 3/4 cup. Stir occasionally while cooking. When reduced, remove from heat and let cool, remove the thyme and bay leaf and discard those.
In a small bowl, mix together the cream, flour, and garlic, mixing well.
When the ale mixture is cool, stir the cream mixture into it.
Preheat your oven to 190° C (375° F). Grease a 9x13 baking dish with butter. Arrange half of the potatoes on the bottom of the dish, overlapping the edges slightly. Sprinkle with salt and pepper as desired.
Pour half the ale mixture evenly over the potatoes, and sprinkle with half the Gruyere cheese.
Repeat with the remaining potatoes, salt and pepper, ale mixture, and cheese. Cover and bake for 30 minutes.
Reduce the oven temp to 180 C (350 F), uncover the baking dish, and bake for another 30 minutes or until the potatoes are tender and the top is golden brown.
Let stand 10 minutes, then serve as a side with any main dish. Enjoy.