Sprinkle the yeast and sugar over 3 tablespoons of warm water in a small bowl. The water should be no more than 100 degrees F (40 degrees C).
Let stand for 5 minutes until the yeast softens and begins to form a creamy foam.
Combine the pumpkin, 1 cup of flour, brown sugar, salt, cinnamon, nutmeg, and allspice in a large bowl.
Mix yeast mixture into the pumpkin mixture; stir until smooth. Beat in the eggs, one at a time. Stir in 2 cups of flour, mixing well after each addition. Stir in the butter a few pieces at a time, beating until incorporated. Stir in the remaining 3/4 cup of flour, mixing until creamy. Lightly oil a large bowl, then place the dough in the bowl and turn to coat with oil. Cover with a light cloth and let rise in a warm place (80 to 95 degrees F (27 to 35 degrees C)) until doubled in volume, about 3 hours. Gently deflate the dough, then cover tightly with plastic wrap. Refrigerate overnight.
Lightly grease a 9x5-inch loaf pan. Deflate the dough and turn it out onto a lightly floured surface. Use a knife to divide the dough into eight equal pieces-don't tear it. Shape into dough rounds and let rest for 10 minutes. Form the dough into balls, and place each ball into the prepared pan, making two rows of four balls.
Whisk the egg yolk and milk together in a small bowl.
Brush the top of the dough with the egg wash, then cover the loaf with a damp cloth and let rise until doubled in volume, about 40 minutes.
Preheat an oven to 400 degrees F (200 degrees C).
Bake in the preheated oven for 20 minutes. Reduce heat to 350 degrees F (175 degrees C) and continue baking until the top is golden brown and the bottom of the loaf sounds hollow when tapped, 10 to 15 minutes. Cool in the pan for 10 minutes before removing to cool completely on a wire rack.
