Gluten-Free Vollkornbrot (German Bread)

Stir together 1/3 cup boiling water and oat groats in a small heatproof bowl. Cover and let stand at room temperature until water is absorbed and groats are softened slightly, 12 to 16 hours.

Combine buckwheat groats, flax seeds, pepitas, sesame seeds, and sun- flower seed kernels in a large nonstick skillet. Cook over medium, shaking skillet often, until groats and seeds are toasted and fragrant, 5 to 7 minutes. Transfer mixture to a medium bowl; let cool 10 minutes. Stir in 3/4 cup room-temperature water. Cover and let stand at room temperature until water is absorbed and seeds are softened slightly, 12 to 16 hours.

Stir together 1/2 cup room-temperature water and gluten-free starter in a small bowl until starter is mostly dissolved. Add white rice flour and teff flour; stir until smooth. Cover and let stand at room temperature until risen slightly and cracked on top, 12 to 16 hours.

Make the dough: Stir together levain, white rice flour, teff flour, 1/3 cup room-temperature water, buckwheat flour,and molasses in a large bowl until dry ingredients are well combined. Cover with a clean towel, and let stand at room temperature 10 minutes.

Sprinkle dough with salt. Grab a portion of dough along the side of the bowl, and bring it toward the center. (Dough will feel like wet sand.) Continue this motion for 1 minute, rotating bowl 90 degrees after each fold. Cover and let rest 2 minutes. Repeat folding process for 1 minute. Set aside. Pour oat groat soak through a fine wire-mesh strainer into a sink to drain any water that wasn't absorbed. Add drained oat groat soak and seed-and-groat mix to dough in bowl. Mix using your hands until seeds and groats are evenly incorporated.

Coat an 8 1/2- x 4 1/2-inch loaf pan with cooking spray. Line pan with parchment paper, leaving a 1-inch overhang on long sides of pan. Lightly coat parchment paper with cooking spray. Pour dough mixture into prepared pan, and smooth top. Sprinkle evenly with mixed buckwheat groats and seeds. Let stand, uncovered, at room temperature until dough rises to top of pan, 4 to 5 hours. During final 30 minutes of proofing time, preheat oven to 350°F.

Bake loaf in preheated oven until set and internal temperature registers 205°F, 1 hour and 20 minutes to 1 hour and 30 minutes, tenting with aluminum foil after 55 minutes if needed to prevent overbrowning. Remove from oven. Let loaf cool in pan 10 minutes. Remove loaf from pan using parchment overhang as handles. Transfer to a wire rack, and let cool completely, about 2 hours. If desired, serve with orange marmalade.