In a bowl, combine 1-1/2 cups flour and yeast; set aside. In a saucepan, heat and stir pumpkin, milk, sugar, 2 tablespoons butter and salt until warm (120°-130°) and butter is almost melted. Add to flour/yeast mixture along with egg. Beat on low speed for 30 seconds. Beat on high speed for 3 minutes. Stir in enough remaining flour to make a moderately stiff dough.
Knead on a lightly floured surface until smooth and elastic, about 6-8 minutes. Place in a greased bowl, turning once to grease top. Cover and let rise until doubled, about 1 hour. Roll into a 12-in. x 10-in. rectangle. Melt remaining butter; brush on dough. Combine brown sugar and cinnamon; sprinkle over dough. Roll dough, jelly roll style, starting with the longer side.
Cut into 12 slices, 1 in. each. Place rolls, cut side down, in a greased 13x9-in. baking pan. Cover and let rise until doubled, about 30 minutes. Bake at 375° for 20-25 minutes or until golden brown. Cool on a wire rack.
For frosting, melt butter in a saucepan; stir in brown sugar and milk. Cook and stir over medium-low heat for 1 minute. Stir in vanilla, salt and 1/4 cup confectioners' sugar; beat until well blended. Add more sugar, if necessary, to achieve desired consistency. Drizzle over rolls.