Cinnamon Brioche

Add the sponge ingredients to the bowl of a stand mixer. Mix until well combined. Cover and let stand for about an hour until bubbly.

To the sponge add everything but the butter. Mix with dough hook until combined, then increase speed to medium and knead until the dough pulls from the sides forming a mass on the hook (20 to 30 minutes).

Start adding butter a tablespoon at a time. Each addition should get fully incorporated before adding the next. This takes at least 15 minutes. Continue kneading until the dough passes the windowpane test (about 15 minutes). Cover and let rise until doubled in volume, about 90 minutes.

Stir together filling ingredients. Grease two 9×5‑inch loaf pans with butter. Divide dough into 12 equal portions. Flatten each piece into a notecard-sized rectangle, spread 2 teaspoons of filling over top, and fold by thirds like a letter. Re-form the rectangle, sprinkle another teaspoon of filling over top, then roll into a tight cylinder.

Place 6 dough logs into each loaf pan in a single row, seam-side down. Make a little space between logs and sprinkle any remaining sugar in the gap, but not on top where it may burn. Cover and let rise until pans are nearly filled (about 2 hours). Preheat oven to 350° F. Bake for 30 to 35 minutes until deep golden brown. Let cool 15 minutes in the pans.

Whisk together the glaze ingredients. Remove the loaves from the pans. Pour glaze generously over the top, allowing glaze to drip down the sides. Let cool completely.