In a food processor, pulse together all-purpose flour, whole wheat flour, brown sugar, baking powder, and salt until combined. Cut in cold cubed unsalted butter and pulse until the mixture resembles pea-sized crumbs. Add vanilla extract and eggs, mixing until just combined. Shape the dough into a rectangle, wrap it in plastic, and chill in the refrigerator for at least 30 minutes.

While the dough chills, prepare the strawberry filling by combining fresh strawberries, Medjool dates, spiced rum, honey, lemon zest, lemon juice, and a pinch of ground cinnamon in a saucepan. Cook over medium heat, stirring occasionally, for about 10-15 minutes until the mixture has thickened and the strawberries have softened. Blend the mixture until smooth, then set aside to cool slightly.

Preheat your oven to 350°F (175°C). After the dough has chilled, roll it out on a floured surface into a rectangle about 1/4 inch thick. Cut the dough into equal-sized rectangles and pipe or spoon the strawberry filling down the center of each piece. Fold the edges over to enclose the filling, making sure to seal the seams well to prevent leaking during baking.

Carefully place the assembled bars seam side down on a lined baking sheet. Bake in the preheated oven for 18-22 minutes or until the bars are lightly golden brown and fragrant. The edges should be firm, giving a slight resistance when pressed lightly.

Once baked, remove the Homemade Strawberry Nutrigrain Bars from the oven. Allow them to cool on the baking sheet for about 10 minutes, then transfer to a wire rack to cool completely. Once cooled, slice into bars and store in an airtight container.