Heat oven to 350°F (175°C). Line an 8-inch square pan with parchment paper, leaving overhang.
In a large bowl, stir melted butter and brown sugar until combined. Add egg and mix until smooth.
Add flour, rolled oats, baking powder, and salt. Stir until a thick, crumbly dough forms.
Press about two-thirds of the dough firmly into the prepared pan to form an even base.
Spread raspberry jam evenly over the base.
Crumble remaining dough over the jam in small pieces.
Bake 25–30 minutes, until lightly golden and the jam looks set.
Cool completely (at least 1 hour). Lift out using parchment and slice into bars.