In the bowl of a freestanding electric mixer, whisk together 3/4 cup warm whole milk with 1 teaspoon granulated sugar. Sprinkle 2 1/4 teaspoons active dry yeast over the milk and gently whisk the mixture again until all the yeast granules are wet. Set aside and let stand for 10 minutes.
Meanwhile, combine remaining 1/2 cup granulated sugar, 1 cup pumpkin puree, 1/4 cup melted butter, 3 eggs, and 1 teaspoon kosher salt. Whisk together until the ingredients are combined and the mixture is smooth and a homogenous pale orange color.
Return to your milk and yeast mixture — at this point it should be frothy and bubbly. Sprinkle 2 cups all-purpose flour over the mixture and use the mixer's paddle attachment to beat the flour into the yeast mixture on the mixer's lowest setting. Once the flour has been incorporated into the yeast, beat in the pumpkin mixture (from the 2nd step). Keep the mixer on its lowest setting and start adding the remaining 4 cups of flour one cup at a time until a dough comes together. At this point, use a rubber spatula to scrape down the paddle attachment and the sides of the bowl and switch to the mixer's dough hook attachment. Knead the dough on the mixer's lowest setting until the dough is smooth and elastic, about 5 minutes. The dough should pull away from the sides of the bowl, but still be a little sticky at the bottom.
Transfer the dough to an oiled bowl, turning the dough to coat completely with oil. Cover with plastic wrap and allow the dough to proof in a warm place until doubled in volume, about 1 1/2 hours.
As the dough is proofing, make the filling. Place 1/2 cup unsalted butter into a lightly colored, heavy-bottomed pan over medium-low heat. Melt the butter, swirling the pan occasionally, until the butter starts to foam and splatter. Use a heatproof rubber spatula to scrape the sides and the bottom of the pan occasionally to prevent the butter from burning. After around 5 minutes, golden flecks should appear in the butter, and the butter should smell nutty and toasted. When scooped into a white plate, the butter should be a light to dark brown amberish color. Remove from heat and allow to cool to room temperature completely on a wire rack.
In a medium bowl, whisk together 1 cup dark brown sugar, 1 tablespoon ground cinnamon, 1 teaspoon ground ginger, 1/2 teaspoon ground nutmeg, 1/2 teaspoon ground cloves, a pinch of allspice, and a pinch of kosher salt.
Return to your dough. Once the dough has doubled in size, transfer to a lightly floured counter and use a rolling pin to roll into a rectangle about 16 x 24 inches.
Use a pastry brush to brush the rolled dough with the brown butter (from the 6th step). Sprinkle heavily with the sugar and spice mixture (from the 7th step).
Working lengthwise, roll the dough into a log, pinching its edges to seal. Cut the roll into 12 pieces, each about 2 inches wide. Place the cut-sides down on a parchment-lined 18 x 12-inch jelly roll sheet pan, spaced 3/4 inches apart. If you don't have a jelly roll sheet pan that large, you can use two 13 x 9-inch sheet pans. Cover loosly with plastic wrap and let rise in a warm place until the edges of the roll are rounded and touching, around 1 hour.
As the rolls are rising, preheat the oven to 350 (F). Bake in the preheated oven for around 20 to 25 minutes, or until the edges of the bun are golden orange in color. Transfer to a wire rack to cool.
While the rolls are cooling, make the crème fraîche glaze. Combine 3 ounces crème fraîche and 2 tablespoon milk in the bowl of a freestanding electric mixer fitted with a paddle attachment and beat on a low speed until combined. Add 1 1/2 cups confectioner's sugar all at once and beat until fluffy and of drizzling consistency. Use immediately to drizzle on top of each cinnamon roll while the rolls are still warm, using a rubber spatula or knife to spread out the glaze as it melts from the warmth of the rolls.