Proof yeast: Heat the milk until lukewarm (body temperature). Mix with the yeast and let stand for about 5 minutes until the mixture is foamy. Melt the butter and let cool slightly until needed.
Mix: In the food processor, mix the flour, sugar, and salt. Add the melted butter, eggs, milk, and yeast mixture.
Knead with the kneading attachments until the dough is smooth and it doesn't stick anymore. Add 1 or 2 teaspoons extra flour if the dough is too sticky, but not too much; the dough should still be soft.
Let rise: Transfer the dough to a bowl, cover it with a clean kitchen towel and let rise in a warm spot for about ½ to 1 hour or until doubled in size.
Peel the apples, remove the core, and chop the apples into small cubes. Turn them into the lemon juice to avoid them browning. Melt the butter and mix it with brown sugar and 1 teaspoon cinnamon.
Knead the dough very shortly and roll it to a rectangle on the lightly floured surface. The rectangle should be about ½ cm/ 0.4 inch thick, as long as the loaf pan and 3 times as broad as the loaf pan.
Fill: Spread about ¾ of this butter-sugar mixture on the rectangle and sprinkle about ¾ of the chopped walnuts on top.
Cut the rectangle into 3 long strips. Cut each of these strips into 4 squares; you should have 12 of them. Prop the loaf pan against the wall or another larger object; it should stand.
Start to staple the dough squares in the pan, placing a few apple cubes on each square except the very last one. Place the loaf pan on the working surface again, shake gently to help the squares spread evenly in the pan.
Let rise: Cover the loaf pan with the kitchen towel again and let rise for about 20 minutes. In the meantime, preheat the oven to 180 degrees Celsius/ 360 degrees Fahrenheit.
Top: Spread the rest of the butter-sugar-cinnamon mixture on top of the bread. Sprinkle with the remaining chopped walnuts and top with the remaining cubed butter. Sprinkle with the rest of the cinnamon and brown sugar.
Bake for about 30 minutes until the bread is cooked through but still soft. If the top of the bread gets too dark too soon, place a piece of aluminum foil on top. The bread tastes best when very fresh and still a bit warm.
You can use fresh yeast (about 15 g/ 0.5 oz) or instant dry yeast as well. Proof the fresh yeast like you would proof the active dry yeast. Instant dry yeast can be mixed directly with the dry ingredients.