Stir flour, oats, brown sugar, baking powder, and salt in a bowl.
Mix until clumpy and sandy. It'll look like damp granola—perfect.
Press about two-thirds into your pan to form an even base. Save the rest for the crumble.
Warm it slightly if thick. Dollop and spread gently so you don't pull up the base.
Pinch the reserved mixture into small clusters and scatter. Leave some jam peeking through for drama.
350°F (175°C) for 25–32 minutes, until edges turn golden and the top feels set.
Seriously, let them cool. They slice clean when cool and hold together better. I know, patience—rude.