Æblebrioche

No, that is normal: the apple pieces are worked into the already risen dough, and they release juice as you fold them in. Use only 1-2 small apples as stated and dice them finely so they distribute without watering down the dough. If it gets hard to handle, dust your hands and the work surface with a little flour rather than kneading extra flour into the whole batch, which would make the brioches dry.

Yes. For fresh yeast, use about half a cube (roughly 20 g) crumbled into the lukewarm milk with 1 tsp sugar, exactly as the recipe starts the pre-ferment. Instant yeast can be mixed straight into the flour, but then let the dough rise a bit longer before shaping so it still doubles in the warm place.

A firm, slightly tart apple holds its shape best, since the pieces bake inside the dough for 20-25 minutes and softer varieties can turn to mush. The recipe calls for peeling, coring and dicing, and peeling is worth keeping - skins stay chewy in a soft brioche crumb. Cut the dice small so each of the roughly 9 portions gets fruit.

Keep them in an airtight container at room temperature; they are best on the day of baking, because the apple pieces make the crumb moist and they soften quickly. Dust with powdered sugar only right before serving, as it dissolves on standing. For a head start, you can let the kneaded butter dough rise slowly in the fridge overnight, then bring it to room temperature before working in the apples and shaping.

The two most common causes are milk that was too hot when activating the yeast and a rising spot that was too cool - the milk should be lukewarm and the dough needs a genuinely warm place. Adding the 40 g soft butter too early or all at once also slows the yeast, which is why it is kneaded in gradually at the end. Finally, be gentle when working in the apples: the dough is only flattened with your fingers, not kneaded hard again, so the gas built up during rising is not pressed out.