Preheat oven to 400°F. Line a rimmed baking sheet with parchment paper. Stir together granulated sugar, baking powder, baking soda, salt, and 3 cups of the flour in a medium bowl. Stir together buttermilk, 5 tablespoons of the melted butter, and 1 teaspoon of the vanilla in a small bowl. Add buttermilk mixture to flour mixture, and stir to combine.
Sprinkle 1/4 cup of the flour on work surface; turn out the dough, and sprinkle with remaining 1/4 cup flour. Knead lightly, using the heel of your hand to compress and push the dough away from you, and then fold it back over itself. Give the dough a small turn, and repeat 8 or so times. (It’s not yeast bread; you want to activate the gluten just barely, not overwork it.)
Using a lightly floured rolling pin, roll dough into a 12-inch square about 1/4 inch thick. Brush dough with remaining 1 tablespoon melted butter. Sprinkle with brown sugar, cinnamon, and 1/2 cup of the pecans. Roll dough into a log, starting with edge closest to you. Pinch seam closed. (It’ll be a bit messy, with filling spilling out. It might also stretch out a bit when you roll it, so push it back together at both ends to return it as close to 12 inches as possible.)
Using a very sharp or serrated knife, cut log into 1-inch-thick slices. Transfer slices to prepared baking sheet. Bake in preheated oven until golden brown, 25 to 30 minutes. (Cover with aluminum foil at the end of baking if the exposed pecans start to darken too much.)
Meanwhile, stir together cream cheese, powdered sugar, softened butter, 1 teaspoon milk, and remaining 1/2 teaspoon vanilla in medium bowl. Beat with an electric mixer at medium speed until smooth and creamy. (Add up to 1 teaspoon more milk, 1/2 teaspoon at a time, and beat until desired consistency is reached.) Spread glaze over warm rolls. Top with remaining 1/4 cup pecans. Serve immediately.