Preheat oven to 350 degrees.
Whisk together the flour, oats, salt and baking soda. Add in 1/2 cup each of sugars and mix until no clumps remain. Combine the melted butter and vanilla and add to crust and crumb mixture. Fold together until evenly moistened.
Gently press about 2/3 of mixture in bottom of a greased 9 or 10-inch square baking dish and bake in preheated oven for 10 minutes.
Meanwhile, in a clean bowl, whisk together the pumpkin filling ingredients: remaining sugars, cinnamon, nutmeg, ginger, cloves, salt, egg and yolk, vanilla, pumpkin and half and half. Be sure to whisk well until mixture is completely smooth.
Remove crust from oven and spread filling evenly over top of the crust. Return pan to oven and bake for 12 minutes more.
Remove pan from oven again and evenly sprinkle the remaining crumb mixture over the top. Bake again for 20-24 minutes, until center only giggles slightly. Remove finished bars from oven and cool in pan on counter for 1 hour. Refrigerate for at least 1 hour before slicing and serving bars topped with whipped cream or ice cream.