Place the uncooked brown rice in a large mixing bowl. Add boiling water to the bowl (enough to cover the rice by about 1 inch / 2.5 cm).
Allow the rice to soak for thirty minutes. (See notes for soaking overnight, instead of a fast soak).
Prepare a 9x5-inch (22.5x12.5 cm) loaf pan. If using a nonstick loaf pan (e.g., silicone), no preparation is needed. Otherwise, line the pan with nonstick parchment paper. If you do not object to oil, spray the pan with nonstick cooking spray, or lightly oil/grease the pan.
Drain the soaked rice through a colander or mesh sieve and rinse under cold water. Gently shake off the excess water.
Scrape the soaked, drained rice into a high-speed blender container (see notes for using a regular blender). Add the 1 and 1/4 cups warm water, coconut sugar, and optional salt. Blend on high speed for 90 to 120 seconds until the batter is silky smooth and very warm (it is very important that the batter be very warm to activate the instant yeast).
Add the instant yeast and baking powder to the blender container. Blend for 15 to 20 seconds until combined.
Pour the bread batter into the prepared pan. Place the pan in a draft-free warm place. Immediately preheat the oven to 350F (180C). Do not hesitate (the bread rises very quickly. The oven needs to be hot and ready to go as soon as the bread hits the needed rising mark (see next step).
Let the bread batter rise for 20 to 25 minutes. It happens quickly, so stay close by. The bread is ready to bake as soon as the batter is a short distance away from the the top edge of the pan (the batter should be no closer than 1/4 inch away from the top). (Note: If the batter is all the way to the top, it will overflow the top of the pan once it hits the heat of the oven).
Bake the bread in the preheated oven for 45 to 50 minutes until crusty in appearance and deep golden brown at the edges. The loaf will be flat on top (no peaks in the center) and somewhat pale towards the middle (even when it is completely baked).
Let the loaf cool, in the pan, on a cooling rack for 15 minutes.
Remove the bread from the pan and cool the loaf completely on a wire rack, or other cooling rack.
Slice the bread, thick or (relatively) thin, as desired. The bread is wonderful plain, toasted, as part of a sandwich, or any way that you prefer!