Make the Babka Dough

• In the bowl of a stand mixer fitted with the dough hook, combine the bread flour, sugar, instant yeast, and salt.
• Add the eggs, lukewarm milk, honey, and vanilla. Mix and knead until a shaggy dough forms, then continue kneading for about 4–5 minutes, until the dough begins to smooth out.
• With the mixer running, add the softened butter a little at a time, allowing each addition to incorporate before adding more.
• Once all the butter has been incorporated, continue kneading for 7–10 minutes, or until the dough is smooth, glossy, stretchy, and slightly tacky.
• Transfer the dough to a lightly greased bowl, cover, and let rise in a warm place for 1½–2 hours, until noticeably puffy.
• Refrigerate the dough for 30–45 minutes. Chilling makes the enriched dough much easier to roll, fill, and twist.

Make the Honey-Cinnamon Apple Filling

• While the dough rises, peel and core the apples. Dice them very finely, approximately ¼-inch pieces. Do not grate them; you want small pockets of apple throughout the babka.
• Melt the butter in a large skillet over medium heat.
• Add the diced apples, brown sugar, honey, cinnamon, and salt. Cook for 8–12 minutes, stirring frequently, until the apples have softened and most of the liquid has evaporated.
• Mix the cornstarch with the lemon juice until smooth. Stir it into the apples and cook for another 1–2 minutes, until the filling is thick and jammy with no watery liquid pooling in the skillet.
• Remove from the heat and stir in the vanilla.
• Spread the filling onto a large plate or shallow dish and allow it to cool completely before assembling the babka.

Make the Cinnamon Streusel

• Combine the flour, brown sugar, cinnamon, and salt in a small bowl.
• Add the cold butter and rub it into the dry ingredients with your fingertips until irregular, chunky crumbs form.
• Refrigerate until ready to use.

Assemble the Babka

• Line a 9 × 5-inch loaf pan with parchment paper, leaving enough overhang to help lift the baked babka from the pan.
• On a lightly floured surface, roll the chilled dough into approximately a 12 × 16-inch rectangle.
• Spread the completely cooled apple filling evenly over the dough, leaving approximately a ½-inch border around the edges.
• Starting from one of the long sides, roll the dough tightly into a log.
• Transfer the log to the refrigerator and chill for 15–20 minutes. This makes it considerably easier to cut and twist without losing all those beautiful apple layers.
• Using a sharp knife, cut the log lengthwise down the center, exposing the apple-filled layers.
• Position both halves with their cut sides facing upward. Twist the two pieces around each other 3–4 times, keeping the exposed apple layers facing upward as much as possible.
• Carefully transfer the twisted babka to the prepared loaf pan, tucking the ends underneath if necessary.
• Scatter the chilled cinnamon streusel lightly over the top. Don't pack it into the openings; you want to see the twisted dough and apple filling underneath.

Proof and Bake

• Cover the loaf loosely and let it rise in a warm place for 45–75 minutes, until noticeably puffy. It does not need to double in size.
• Meanwhile, preheat the oven to 350°F.
• Place the loaf pan on a baking sheet to catch any filling that may bubble over.
• Bake for 40–50 minutes. Check the babka at approximately 30 minutes; if the top is becoming too brown, tent it loosely with aluminum foil.
• The babka is ready when the dough in the center registers approximately 190–195°F on an instant-read thermometer. Insert the thermometer into a doughy section rather than directly into the apple filling.
• Let the babka cool in the pan for approximately 15 minutes, then carefully lift it out using the parchment and transfer it to a wire rack.
• Cool completely before slicing so the crumb and apple filling have time to set.