Pour the lukewarm milk into the bowl of a stand mixer fitted with the dough hook attachment. Dissolve the yeast in the lukewarm (90°F) milk. Cover and let sit until the yeast is foamy, about 5 to 10 minutes.
On low speed, add the sugar, flour, butter, egg and a pinch of salt and knead until a soft dough forms about 5 minutes. Transfer the dough to a lightly floured surface and knead with your hands for one more minute. Sprinkle the dough with a little bit more flour if it's too sticky.
Transfer the dough to a lightly greased bowl, cover and let the dough rest at a warm place for 40 minutes or until about doubled in size.
Make the cinnamon butter: Mix the soft butter, sugar, and cinnamon until fluffy with a handheld mixer or a fork.
Prepare the apples: Peel, core, and slice the apples (1/2 inch thick). Mix with lemon juice.
Grease a 9x13-inch baking sheet. With floured hands spread the dough evenly about 0.2 to 0.4 inch high.
Spread the cinnamon butter on top of the dough, then arrange the apples on the dough like you see in my photos.
Cover the cake with a clean towel and let it rise for about 20 minutes while you preheat the oven to 390°F (200°C).
Bake the apple cake for 25-30 minutes.
While the cake bakes make the topping: In a small, dry frying pan, toast pine nuts until they are golden and give off a light fragrance. Add honey, butter and the chopped rosemary (optional), lightly heat the mixture, then turn off the heat. Spoon this mixture evenly over the cake whilst it is still hot.