Remove the pits from the dates and cut them in half. In a medium saucepan, combine the dates, brown sugar, water, and vanilla extract.
Bring to a simmer to dissolve the sugar. Stir constantly and simmer for one minute.
Let the mixture cool and then purée it into a thick paste.
Crumb Layer
Position oven rack in middle position and preheat oven to 350.
Butter a 9 x 13 pan.
Combine all crumb layer ingredients in a food processor and blitz until it becomes coarse crumbs.
Firmly press half the mixture into the bottom of the greased 9 x 13.
Spread all the puréed date layer over the bottom crumb layer. It will be sticky and difficult to spread evenly without disrupting the bottom crust layer. Work slowly and deliberately.
Sprinkle the rest of the crumb crust on top of the date layer. Press lightly.
Bake about 40 minutes, until the top is golden brown.
Let it cool in the pan, then cut into squares.
Garnish with powdered sugar if desired.
Notes
Sprinkle with powdered sugar right before serving. Travels well. Safe to eat if left on the counter for several days.