To prepare the maple date filling, add all ingredients to a small saucepan and bring to a boil. Immediately, reduce to a low simmer and cook stirring often and taking care that the filling does not scorch. As the dates soften, break them up using the back of a wooden spoon. The filling will be done when the water has evaporated and you can draw the filling into a pile and it will stay without running back down.
Preheat oven to 350 degrees (175c) .
To make the cookie dough, cream the butter and brown sugar together. Add the egg and vanilla and continue to beat until light and fluffy.
Take the oats and place in a food processor, mini chopper or blender, pulse a few times until you get coarse crumbs. Do not blend so much you end up with oat flour. In a separate bowl, combine the oats with the pastry flour, salt, and baking soda.
In halves, add the dry mix to the wet using your mixer. The last half will be quite stiff and should even form a ball. Chill the ball for 15 minutes.
Roll out dough until quite thin. Since these have a top and bottom you will skill have enough cookie in each bite. Using a cookie cutter you can cut out 1 1/4 to 1/12 inch circles. Place half the circles onto the baking sheet, topping each with a rounded teaspoon of the date filling. Top with another circle and press around the edges and even give the top a light pat. (Since I'm never quite sure of the exact yield when I get close to the end of the dough I make just 1 or 2 at a time so there are definitely enough tops to match the bottoms.)
Alternately, you can use a larger cutter, about 1 1/2 - 2 inches, and place the just off center and fold over for lovely crescent shaped cookies.
Bake for 10-12 minutes. Remove from oven and place on cooling rack to cool. Warning: filling is VERY hot when first taken from oven. Use caution if you decide not to wait.