In a small bowl, stir the yeast into the warm water along with the coconut sugar. Let sit 5–10 minutes, until the surface looks foamy and alive.
In a large mixing bowl, combine the flour, sea salt, and chopped rosemary. Pour in the melted butter, then add the activated yeast mixture.
Cover the bowl with a clean kitchen towel and let the dough rise at room temperature for 1–2 hours, until doubled in size.
Once doubled, preheat your oven to 450°F (232°C). Lightly grease a bread pan or line it with parchment. Gently transfer the dough into the pan, smoothing the top lightly with damp fingers if needed.
Cover the pan loosely with foil or an oven-safe lid and bake for 30 minutes. This traps steam, keeping the crumb tender.
Remove the cover and bake an additional 10–15 minutes, until the top is deeply golden and the loaf sounds hollow when tapped. For extra aroma, brush the top with a little melted butter as soon as it comes out of the oven.