Prepare 6 apples: quarter, peel, and core 5 of them and slice into even pieces; grate the first half of the 6th apple on a coarse grater and dice the second half
Cook 5 sliced apples with 1 vanilla pod, 3 tablespoon sugar, and 1 tablespoon lemon juice in a saucepan on medium heat until soft (about 15-20 minutes)
Remove vanilla pod and blend cooked apples into a smooth puree using a hand blender, then let cool (save vanilla pod for reuse)
Mix grated and diced apple with lemon zest and set aside
Peel 800 g floury potatoes; if using fresh bay leaves, cut them along the grain several times to release more flavor; cook potatoes in salted water with 3 bay leaves on medium-high heat until soft (25-30 minutes)
Drain potatoes, return to pot, add 50 ml cream and 100 g butter, mash with potato masher until chunky (avoid overmixing, which makes it slimy), season with salt, pepper from the mill, and a pinch of fresh nutmeg to taste
Dice 100 g bacon finely and slice 3 onions into fine rings
Cook bacon in a pan on medium-high heat, stirring frequently, until starting to crisp; add onion rings and fry together until golden brown and crispy (about 10-15 minutes), then keep warm
Heat a pan with a little oil; cook 4 sausages on medium-low heat with the lid on, turning occasionally, until the internal temperature reaches 63°C / 145°F (about 10 minutes)
Remove lid, increase heat to medium-high, and fry sausages turning more frequently until the exterior is crispy at contact points (about 5-8 minutes more)
Warm 4 serving plates; divide mashed potatoes among them, top with bacon-onion mixture and its rendered fat, place a sausage on top of each portion
Garnish with finely chopped parsley (including stems) and serve immediately with 1 glass aquavit per person