For the custard, in a medium saucepan, combine milk, cream, buttermilk, pumpkin, sugars and pumpkin pie spice. Heat on low until sides of pan are slightly bubbly and warm, but not boiling. Add 1/4 cup of the milk mixture to the egg yolks and stir quickly, keep adding small amounts of liquid to the eggs until it it the same temperature as what is in the saucepan. Add egg yolk mixture to the saucepan and continue to heat until you can coat the back of a spoon. Do not boil!! Remove from heat and cool, preferably into a pourable bowl. Refrigerate until completely cold, preferably overnight.

For the streusel, combine brown sugar, flour and cinnamon in a bowl. Cut in butter until mixture resembles coarse crumbs. Stir in pecans. Coat a 9 x 9 or 8 x 8 baking dish with cooking spray. Press mixture into pan and bake for 12-15 minutes or until edges are browned. Cool completely and break into pieces. Set aside.

Churn cream mixture into ice cream, when almost done, pour streusel into machine until mixed. Spoon ice cream into a freezer container. Cover; freeze overnight.

Serve ice cream sprinkled with turbinado sugar.