Preheat your oven to 425 degrees. Place the yeast, sugar and warm water into a large mixing bowl and watch it proof for a few minutes. When bubbles are seen, add the salt and flour, adding the last cup a bit at a time, kneading it well to form workable dough. Work the dough for 10 minutes, then cover the bowl with a damp towel, and let it rise in a warm place until doubled in bulk, about 1 hour. Punch down the dough and form it into balls about 2” in diameter. Roll these out between the palms of your hands and the work surface to form ropes, then join the ends of these ropes to form crown shapes and place them onto a baking pan lined with parchment paper. Using clean scissors, cut X’s into the crowns to give them a thorny appearance. Be sure to go all the way around your crowns. Once they have been “thorned”, leave them on the baking pan to rise for about 15 more minutes while you put a shallow pan of water on to simmer gently. Add the baking soda, once the water has begun to simmer, then lower each crown into the soda water and blanch it for 1 minute. When you remove it from the water and place it back on the baking sheet, immediately sprinkle it with a little bit of coarse salt. Once all the crowns have been blanched, bake them for about 8-10 minutes until done.