Preheat oven to 300℉.

In a food processor blend dates with dark brown sugar. Add very hot water. Blend until smooth. Temper with eggs by adding some hot water slowly while whisking eggs before adding to the food processor. Add melted fat. Add flour, baking powder, vanilla and salt, blend until smooth. 

Pour in to a 9.5 inch X 15.25 inch pyrex and bake covered for 25 minutes. Remove the cover and bake 8 more minutes.

Heat the cream and banana puree to boil and set aside.

Heat the corn syrup and add sugar a little at a time to make a dark amber caramel.  Deglaze with the hot cream and banana puree liquid (carefully!) and blend with a hand blender. Cool before use.

Serve a piece of cake with a generous serving of banana toffee sauce.  Add ice cream if desired.