Preheat your oven to 350°F (175°C). Prepare an 8x8-inch baking pan by greasing it or lining it with parchment paper.

Combine the dry ingredients in a large mixing bowl. Mix together the all-purpose flour, rolled oats, brown sugar, baking powder, and salt until well blended.

Add the cold, cubed butter to the dry ingredients. Blend until the mixture resembles coarse crumbs, about 3-5 minutes.

Reserve about 1 cup of the crumble mixture for topping the bars later. Keep it aside in a small bowl.

Toss the raspberries with granulated sugar, cornstarch, lemon juice, and vanilla extract. Ensure they are well coated.

Press the remaining crumble mixture into the bottom of the prepared baking pan to create a firm, even layer as your crust.

Spread the raspberry mixture over the crust, ensuring it is evenly distributed.

Sprinkle the reserved crumble mixture on top of the raspberry filling.

Bake in the preheated oven for 30–35 minutes, or until the top is golden brown and the filling is bubbly.

Cool the bars in the pan for about 10 minutes before transferring them to a wire rack to cool completely.

Slice into squares or bars once cooled. For best presentation, use a sharp knife.

Serve and enjoy warmly or at room temperature.