Lightly toast the rolled oats in a dry skillet for 2-3 minutes before mixing into the crumble topping to deepen their nutty flavor and prevent a raw, doughy taste.

Always toss your fresh raspberries with cornstarch and lemon juice before layering to absorb excess moisture and keep the filling from seeping into the oat base.

Cut cold butter into small cubes and work quickly into your oat mixture with your fingertips to create distinct pockets that bake into a delightfully crumbly, chunky texture rather than a dense paste.

Use the bottom of a measuring cup to firmly compress the bottom oat layer before adding filling so it forms a cohesive crust that won't crumble apart when slicing.

Allow bars to cool at room temperature for at least 2 hours (preferably chill for 4+ hours) so the filling sets properly and bars slice cleanly without falling apart.