Seeded Buckwheat Skillet Boule

Method

1. 1Make the psyllium gelWhisk the psyllium, yeast and maple syrup into the warm water. Let it stand about 10 minutes until it thickens into a loose gel and smells yeasty. Water hotter than about 110°F (43°C) will kill the yeast, so check it.
2. 2Mix the dryIn a large bowl, whisk the buckwheat flour, sorghum flour, brown rice flour, tapioca starch, salt, pumpkin seeds and sunflower seeds.
3. 3Bring the dough togetherAdd the gel, vinegar and avocado oil. Mix with a sturdy spatula, then your hands (or a stand mixer with the paddle) for 3 to 4 minutes until it is one cohesive, slightly tacky ball. It won't stretch like wheat dough; that's normal.
4. 4Shape and proofWith wet hands, shape into a tight round, smoothing the top. Set it seam-down on parchment inside a medium bowl, cover, and proof somewhere warm until about 1.5x in size and slightly puffy, about 70 minutes.
5. 5Preheat skillet and steam panWhile it proofs, put the cast iron on the middle rack and an empty sheet pan on the bottom rack. Preheat to 475°F (245°C) for a full 45 minutes so the iron is screaming hot.
6. 6Score and loadDust the top with a little rice flour and slash it about 1 cm deep with a sharp knife. Lift by the parchment into the hot skillet, pour the boiling water into the sheet pan, and shut the door fast.
7. 7Bake with steamBake 20 minutes at 475°F (245°C).
8. 8Finish the bakePull the steam pan, drop to 425°F (220°C), and bake 35 to 40 minutes more, until deep brown and 208°F (98°C) inside. Underbaking is the most common GF failure; go by the thermometer, not the color.
9. 9Cool completelyCool on a rack at least 2 hours before cutting. The crumb is still setting; cut early and it will be gummy no matter how well you baked it.