In the bowl of a stand mixer fitted with the paddle attachment, beat 2½ cups (313 grams) all-purpose flour, whole wheat flour, yeast, and salt at low speed until combined.

In a small saucepan, heat sweet potato, milk, butter, honey, and vanilla over medium heat until butter is melted and an instant-read thermometer registers 120°F (49°C) to 130°F (54°C). Add warm sweet potato mixture to flour mixture, and beat at low speed until combined, about 1 minute.

Switch to the dough hook attachment. Beat until a smooth, elastic dough forms, 12 to 13 minutes; add up to remaining ¼ cup (31 grams) all-purpose flour, 1 tablespoon (8 grams) at a time, if dough is too sticky. Turn out onto a very lightly floured surface, and shape into a smooth round.

Lightly oil a medium bowl. Place dough in bowl, turning to grease top. Cover and let rise in a warm, draft-free place (75°F/24°C) until doubled in size, 45 minutes to 1 hour.

Spray a 9-inch round cake pan with cooking spray.

Punch down dough, and turn out onto a lightly floured surface. Divide dough into 9 portions (about 98 grams each). Shape into smooth rounds, and place in prepared pan. Cover and let rise in a warm, draft-free place (75°F/24°C) until doubled in size, 35 to 45 minutes.

Preheat oven to 350°F (180°C).

Brush top of rolls with egg, and sprinkle with desired seeds.

Bake until deep golden brown and an instant-read thermometer inserted in center registers 200°F (93°C), 25 to 30 minutes. Let cool in pan for 5 to 10 minutes. Serve warm.