Make the dough. Combine all dough ingredients except melted butter in the bowl of a stand mixer fitted with a dough hook*. With the mixer on low speed, slowly add 2 Tablespoons melted butter. Increase speed to medium and mix until a shaggy dough forms.
Transfer the dough to a clean work surface and knead by hand until a smooth dough forms. The dough should be completely smooth and slightly tacky, but not sticky. If needed, add more milk or flour (1 Tablespoon at a time) until you reach the desired consistency.
Transfer the dough to a large, greased bowl and cover with plastic wrap. Let rise 60-90 minutes, or until doubled in size.
Make the filling. While the dough rises, make the filling. In a small skillet over medium heat, melt 1 Tablespoon butter (the remaining softened butter will be used to assemble the layers). Add the diced apples to the skillet and cook, stirring occasionally, until softened, about 3-4 minutes. Remove from heat and stir in 1 teaspoon lemon juice. Set aside to cool.
Grease a 9x5-inch loaf pan and set aside**. In a small bowl, combine the brown sugar, cinnamon, and nutmeg. Stir until combined and set aside.
Shape the dough. After the rise, turn the dough onto a clean work surface and divide into 10 equal-sized pieces. I recommend using a kitchen scale (weigh the full dough, then divide by 10 to determine the weight for each piece. For mine, it was about 65g). Flatten each dough piece with the palm of your hand into an oval shape, approximately 4 inches in diameter. Spread with softened butter, then sprinkle generously with the brown sugar mixture. Add apples to half of the oval.
Fold the piece in half (like a taco), then transfer to the prepared loaf pan, fold-side down on the bottom of the pan. Repeat with the remaining pieces of dough until the pan is filled.
Cover the pan with plastic wrap and let rise 30-45 minutes until puffed. The dough should not rise abve the edges of the loaf pan.
Bake the loaf. Preheat the oven to 350℉ (180℃). Place an empty baking sheet on the bottom rack to catch any drips.
Bake for 30 minutes, then tent with aluminum foil and bake for an additional 20-25 minutes until golden brown. Use a kitchen thermometer to make sure the loaf is fully baked. When finished, the loaf will reach an internal temperature of 200℉ (93℃).The loaf may look like it's done baking after the initial 30 minutes, but it's not! The outside is baked, but the inside is still raw, so make sure to cover with foil and continue baking!Let the loaf cool in the pan for 10 minutes, then transfer to a cooling rack to cool fully.
While the loaf cools, make the glaze. In a small bowl, whisk together the powdered sugar, vanilla extract and milk until smooth. Spoon the glaze over the bread before serving.
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Notes
*This recipe can be made without a stand mixer. To do so, mix the dough in a large mixing bowl with a wooden spoon, then knead by hand. **If you are doubling or tripling this recipe, use 2 (for doubling) or 3 (for tripling) 9x5-inch loaf pans. Continue with directions as written for each loaf. To make this recipe with active sourdough starter, replace the sourdough discard with active starter (200g). You will also need to increase the rise times. Did you love this recipe? Try my Sourdough Discard Garlic Pull Apart Bread and my Sourdough Discard Cinnamon Roll Pull Apart Bread, too!