Combine dry ingredients in a large mixing bowl. Cut in the butter with a pastry blender or fork until crumbly. Stir in the white chocolate chips.
Whisk the buttermilk, pumpkin, and vanilla in a small bowl. Stir in just till mixture is moistened.
On a lightly floured surface, pat dough into a circle, about 3/4″ thick. Cut into eight equal wedges. Arrange on greased cookie sheet, or line it with a silicone pan liner.
Brush tops with milk and sprinkle with cinnamon sugar. Bake at 400° for about 18-20 minutes.
Melt the 1/4 cup of white chocolate at half power in the microwave in a small glass bowl, stirring every 30 seconds till smooth. Drizzle over scones.