1. Preheat your oven to 400°F (200°C). Make sure it's nice and hot before moving forward.

2. Peel the potatoes and slice them thinly, trying to get the slices as uniform as possible.

3. In a pan over medium heat, melt half of the butter. Add the sliced onions and sauté until they are soft and translucent. This should take about 5 minutes, depending on the heat and your desired level of doneness.

4. In another pan, melt the remaining butter over medium-high heat. Add the meat mixture and cook until it's nicely browned, breaking it up into small pieces as it cooks. Season the mixture with salt and pepper to taste.

5. In a greased oven-safe dish, create a layer of sliced potatoes. You can overlap them slightly, but try to keep the layer as even as possible. Next, add a layer of the browned meat mixture, followed by a layer of the sautéed onions. Repeat this process until all the ingredients are used up, finishing with a layer of potatoes on top.

6. In a separate bowl, mix together 250ml (1 cup) of beer, 125ml (1/2 cup) of water, a pinch of salt, and a few grinds of pepper. Pour the mixture over the layered ingredients in the dish, making sure everything is well coated.

7. Cover the dish with aluminum foil and bake in the preheated oven for 40-45 minutes, or until the potatoes are cooked through and the top layer is golden brown.

8. Remove the foil and bake for an additional 10-15 minutes, or until the top layer is nicely browned and crispy.

9. Serve hot, garnished with chopped parsley and accompanied by boiled green beans and melted butter.