Heat the buttermilk to 100-110°F and place it in the bowl of a stand mixer. Sprinkle in the yeast, stir gently, and allow it to bloom for 10 minutes.

Add 3 cups of flour, sweet potato puree, melted butter, sugar, salt, and egg to the yeast mixture. Mix with paddle attachment until a shaggy dough forms.

Switch to the dough hook attachment and begin to mix the dough on medium speed. Slowly add just enough of the remaining flour until a smooth, soft, and elastic dough forms.

Knead the dough until you can pull a windowpane test.

Place the dough into a lightly oiled large bowl. Cover the bowl with plastic wrap and let the dough rise in a warm place for 1 hour, or until it has doubled in size.

Preheat the oven to 375°F. Lightly grease a 13-by-9-inch pan with cooking spray or butter.

Once the dough has doubled in size, dust the top of the dough with flour and turn it out onto your floured work surface. Divide the dough into 12 equal pieces. You can eyeball this, but if you're like me and prefer to use a scale, each should weigh 84g.

Shape each roll into a boule (round) using your thumb as a guide. You want the roll to have a smooth surface, and it should hold its shape when left alone.

Space the rolls evenly apart in the prepared baking dish seam-side down. Cover the pan with plastic wrap and let the rolls rise for 20 minutes until they double in size and are light and fluffy.

While the rolls are final proofing, in a small saucepan over medium heat, melt the remaining 2 tablespoons of butter. Continue to stir over medium-low heat until the butter foams, then begins to turn brown, and a nutty aroma develops. Once golden brown, remove from heat.

Brush the tops of the rolls with the browned butter. Bake for 20 to 25 minutes, or until the rolls are golden brown and baked through. Brush the tops with any remaining melted brown butter, if desired. Allow to cool slightly before enjoying.