Preheat your oven to 350°F (175°C) and line an 8x8 inch square baking pan with parchment paper, leaving an overhang for easy removal.

In a medium saucepan, combine the chopped dates and water. Bring to a boil, then reduce heat and simmer for about 10 minutes, stirring occasionally until the mixture thickens into a paste.

Remove the date mixture from the heat, stir in the vanilla extract, and set aside to cool slightly.

In a large mixing bowl, combine the flour, rolled oats, brown sugar, baking powder, and fine salt.

Add the cold, cubed butter to the dry ingredients. Use a pastry cutter or your fingers to rub the butter into the mixture until it resembles coarse crumbs. Stir in the chopped pecans.

Press approximately two-thirds of the oat mixture firmly into the bottom of the prepared baking pan to form the crust.

Spread the cooled date filling evenly over the bottom crust layer.

Sprinkle the remaining oat and pecan crumble mixture over the top of the date layer, pressing down lightly. Finish by sprinkling the flaky sea salt over the top.

Bake for 35 to 40 minutes, or until the crumb topping is golden brown.

Allow the squares to cool completely in the pan on a wire rack before lifting them out using the parchment paper and slicing into 9 squares.