Preheat the oven to 350°F (175°C). Lightly grease a 9x5 inch (23x13 cm) loaf pan and line with parchment paper leaving a slight overhang for easy removal.

If your psyllium husk is whole, grind it quickly in a spice grinder to a powder for best hydration and texture. Measure ingredients before starting.

Mix dry ingredients

In a large mixing bowl, whisk together the gluten-free all-purpose flour, almond flour, baking powder, baking soda, sea salt, ground psyllium husk, ground flaxseed (if using) and sugar until evenly combined and aerated.

Mix wet ingredients

In a separate bowl or large measuring cup, whisk the eggs until smooth. Add the milk, yogurt, oil, apple cider vinegar and vanilla. Whisk until fully combined and slightly frothy.

Combine and rest

Pour the wet mixture into the dry ingredients. Stir with a rubber spatula or wooden spoon until no large dry streaks remain. The batter will be thicker than typical wheat-bread batter but should be spoonable and spreadable. If it seems extremely stiff, add up to 2 tablespoons more milk.

Rest for hydration

Let the batter rest for 8–10 minutes at room temperature. This allows the psyllium and flours to hydrate and improves crumb structure.

Bake

Transfer the batter into the prepared loaf pan, smoothing the top with a wet spatula. Brush the top with melted butter or oil and sprinkle seeds or oats if using.

Bake in the preheated oven for 45–55 minutes, or until the top is golden brown and a toothpick inserted into the center comes out mostly clean (a few moist crumbs are fine). If the top browns too quickly, tent loosely with foil after 30 minutes.

Cool and serve

Remove the loaf from the oven and let cool in the pan for 10 minutes. Use the parchment overhang to lift the loaf onto a wire rack. Brush again with a little melted butter or oil if desired.

Cool completely (at least 1 hour) before slicing to avoid a gummy texture. Store wrapped at room temperature for 2 days or in the refrigerator for up to 5 days; freeze sliced for up to 3 months.