01 -
Turn the oven on to 175°C so it's nice and hot. Line a square 20 x 20 cm baking pan with parchment or grease it up.
02 -
Toss oats, flour, salt, brown sugar, butter, and baking soda into a medium bowl. Mix it all up using your hands or a fork till it looks crumbly.
03 -
Pop rhubarb, sugar, water, and cornstarch in a saucepan. Keep stirring over medium-high till it’s bubbling, thick, and the rhubarb is soft—should take around 5–10 minutes.
04 -
Pull the pan off the burner then stir in your vanilla. Let the filling hang out for about 10 minutes so it gets a bit thicker and cools off.
05 -
Keep 2/3 cup crumb mix aside. Press the rest flat into the bottom of your prepped pan so there aren’t gaps or thin spots.
06 -
Spoon the cooled rhubarb filling right over that base and spread it out good.
07 -
Now shake the crumb mix you saved all over the rhubarb—go for even coverage.
08 -
Slide it in your oven and bake about 30–40 minutes. It should have a set topping and a golden base.
09 -
Once it's out of the oven, leave it in the pan till it's cool. Then slice it into bars and enjoy.