1. In a small saucepan over medium heat, bring milk, butter and honey to a simmer until an instant-read thermometer registers approximately 120° to 130°F (50° to 55°C), about 3 minutes. Do not let boil.
2. Meanwhile, in work bowl fitted with metal dough blade, process 1½ cups (375 mL) of the all-purpose flour, the whole wheat flour, yeast and salt until well combined, about 15 seconds. With the motor running, slowly pour hot milk mixture through the feed tube into work bowl. With the motor continuing to run, spoon additional all-purpose flour through the feed tube, about ¼ cup (50 mL) at a time, until dough pulls away from sides and begins to gather and a soft, not sticky, dough forms, about 90 seconds. Add sunflower seeds and pulse 5 times.
3. Remove from work bowl and place on a floured surface. Knead until dough is smooth and elastic, 3 to 5 minutes. Shape into a ball. Transfer to a large oiled bowl and turn to coat all over. Cover loosely with plastic wrap. Let dough rise in a warm, draft-free place until double in volume, about 45 to 90 minutes, depending on the humidity and heat factors.
4. Preheat the oven to 35°F (180°C). Punch down dough and form into two round loaves. Place on prepared baking sheet, at least 2 inches (5 cm) apart. Cover with a towel and let rest in a warm, draft-free place until they rise slightly, 20 to 30 minutes. Bake in preheated oven until light brown, 30 to 40 minutes. Let cool on wire rack.
Variation: Add ¼ tsp (1 mL) ground cardamom to the flour mixture.