Preheat the oven to 425°. Into a large bowl, sift the all-purpose flour and baking soda. Stir in the whole-wheat flour, 1/2 tsp. sea salt and the rosemary. Make a well in the center of the flour mixture.
In a medium bowl, whisk 1 3/4 cups milk and 1 cup yogurt. Slowly pour the milk mixture into the well in the flour mixture. Using your hands, gradually mix the flour into the milk until fully blended.
Using lightly floured hands, lift the dough from the bowl and shape it into a 9-inch round. Transfer to a floured baking sheet. Flour a large knife and cut a large X into the top of the dough, cutting about two-thirds of the way through.
In a small bowl, whisk the remaining 2 tbsp. milk and 2 tbsp. yogurt. Using a pastry brush, coat the bread with the milk and yogurt mixture. Sprinkle with the remaining 1 tsp. sea salt.
Bake 20 minutes. Reduce the heat to 375° and bake until the top is dry and deep golden brown and the bread sounds hollow when tapped on the bottom, about 35 minutes. Let cool on a wire rack, at least 2 hours.