Cut bread into 1½ inch squares. Place in a greased 9x13 pan.
In a bowl whisk together eggs, milk, pumpkin pie spice, pumpkin puree, heavy cream, sugar and vanilla. Once it's mixed well, pour over bread chunks and refrigerate over night. If looking to do this quicker, refrigerate for at least 30 minutes.
To make streusel, mix flour, brown sugar, cinnamon, pumpkin pie spice and salt in a bowl. Cut in a cold stick of butter. Mix with your fork until crumbly. Refigerate overnight as well.
Once ready to bake preheat oven to 350.
Before baking spread streusel over the top and bake for 35-45 minutes.
Make buttermilk syrup by melting butter in a pan on low-medium heat. Add sugar, buttermilk, vanilla and cinnamon - mix with whisk. Add baking soda and stir until all combined. Well be foamy at first and will then return to normal.
Serve warm with french toast bake right out of the oven.