Dissolve yeast in lukewarm water in a bowl. Let stand until the yeast softens and begins to form a creamy foam, about 20 minutes.
Mix flour, salt, butter, 1 cup white sugar, eggs, and yeast mixture, respectively, in a large bowl. Stir in scalded milk and pumpkin puree until dough consistency is reached. Shape dough into a ball and place in a bowl; cover bowl with a towel. Let rise for 90 minutes.
Shape dough into 2 dozen knotted rolls; arrange on a baking sheet. Let rise again for 30 minutes.
Preheat oven to 350 degrees F (175 degrees C).
Whisk egg yolk with 1/2 teaspoon white sugar until dissolved; brush tops of rolls.
Place baking sheet on the bottom rack of preheated oven; bake rolls for 10 minutes. Transfer baking sheet to top rack; bake until rolls are lightly browned, 6 to 10 more minutes.