Heat the olive oil in your pot and cook the onions until softened.
Add the sausages to the pot, and then the beer (I used the whole thing with a few swigs removed). Sprinkle with salt and pepper, and put the lid on.
Let this boil away on medium-high heat until the grill is ready and the sausages are cooked through, about 15-20 minutes.
Throw the sausages on the grill to get crispy, about 10 minutes over high heat.
Meanwhile, let the onions and beer continue to cook down to a thickened saucy onion topping, which should be done at the same time as your sausages are grilled.