Preheat oven to 350ºF (180ºC). Line a 12 x 18" (30 x 45 cm) baking sheet with parchment paper.
Place the butter, both flours, sugar, salt, baking powder and baking soda into the bowl of a food processor (or use a pastry blender). Process until the mixture is very fine. Transfer to a large bowl and add the pecans and dates. Pour the cream and vanilla over the top. Mix with a fork until a crumbly dough forms.
Turn onto a work surface. Press the mixture together very lightly - it should be fairly dry. Cut into twelve 2 1/2" rounds (7 cm) or eighteen 1 1/2" rounds (4 cm). Place on the prepared pan. Brush with cream and sprinkle with sugar.
Bake for 20 to 25 minutes until golden. Serve warm. Best served the day they are made.