Put the water, yeast and sugar in a large mixing bowl. Combine these ingredients lightly with a fork and let sit for about 15 minutes, or until the mixture begins to foam up and small bubbles appear.
Mix the oil, honey and 2 of the eggs in a small bowl. Pour this mixture into the large bowl when the yeast mixture is ready, then whisk everything together. Stir the ingredients with a rubber spatula while you gradually add in the flour, salt, garlic powder and chopped rosemary until everything comes together. Finish with kneading the dough by hand for a few minutes until the dough is smooth.
Lightly oil a large bowl, put your dough ball into it and turn the dough so its entire surface is covered lightly in oi. Cover the bowl with a clean towel and allow it to rest in a warm place until doubled in size, about 1-1/2 hours.
Punch down the dough and divide it in half if you are going to make two loaves. For 1 large loaf, use 3, 4 or 6 braids. For 2 smaller loaves, use 3 or 4 braids for each loaf.
Preheat the oven to 350° F. Place your challah(s) on a baking sheet. Whisk the remaining egg and brush challah(s) with it. Sprinkle with salt and chopped rosemary. Put the sliced garlic in the areas between the braids. Rest the bread for 30 minutes.
Bake the challah(s) about 30 minutes, or until the internal temperature is 190° F.
After the bread has cooled, garnish with rosemary sprigs.