Parboil the potatoes to give them a head start. Bring a pot of salted water to boil, and after scrubbing and cutting the potatoes so they’re all about the same size (½ or ¼) drop them in the pot for a few minutes.
While the potatoes are parboiling add some water to a shallow pan and poach the sausages (gives them a head start so they aren’t going into the oven raw). Cook for about 2 minutes and when the color has turned from pink to grey and opaque, flip and cook another 2 minutes. While the sausages and potatoes are cooking roughly cut a red onion or 2 and add to a large skillet.
Drain the potatoes and add them to the skillet with the red onion. Drain, or simply grab the sausages out of their cooking water with tongs and add them to the skillet. Drizzle everything with olive oil, season with salt and pepper and add fresh thyme and rosemary (to easily remove the leaves from the stalk: pinch one end of the stem, and then backcomb your fingers and the leaves fall right off.)
Pop the skillet into a 400F oven and allow to cook for about 20 minutes before stirring, giving everything a good shake and turning the sausages. Cook for another 10-15 minutes or until the potatoes are tender and the sausages are cooked through and going crispy on the edges.