Preheat your oven to 350°F (175°C).

Cream together the softened unsalted butter and granulated sugar using an electric mixer on medium speed for about 3 to 5 minutes.

Incorporate the large egg and vanilla extract into the creamed mixture, beating until well combined.

In a separate bowl, whisk together the all-purpose flour, baking powder, and salt. Gradually add this to the wet ingredients and mix until just combined.

Gently fold in the rolled oats and brown sugar until a crumbly dough begins to form.

Lightly grease a 9x13 inch baking dish. Press half of the cookie mixture into the bottom of the dish.

Spread the raspberry jam evenly over the cookie crust.

Sprinkle the remaining crumb mixture evenly over the raspberry jam and press down gently.

Bake for 25 to 30 minutes until golden brown and the edges are slightly crisp.

Allow the cookies to cool in the pan for 10 to 15 minutes before transferring to a wire rack to cool completely.