01 -
Preheat oven to 175°C (350°F). Grease a 9×13 inch baking pan or line with parchment paper for easy removal.
02 -
In a large bowl, mix the rolled oats, all-purpose flour, brown sugar, baking powder, cinnamon, and salt.
03 -
Pour melted butter into the dry mixture and stir until combined. The mixture should appear crumbly and slightly wet, resembling wet sand.
04 -
Press two-thirds of the crumb mixture evenly into the prepared baking pan.
05 -
If using fresh rhubarb, toss it with water to introduce moisture. Spread the chopped rhubarb evenly over the base layer in the pan.
06 -
Sprinkle the remaining crumb mixture evenly over the rhubarb layer to cover it completely.
07 -
Bake in the preheated oven for 30–35 minutes, or until the top is golden brown.
08 -
Allow the bars to cool in the pan completely before slicing into squares.