A delightful dessert combining the tangy flavor of rhubarb with a sweet, crumbly oat topping.
Combine the flour, oatmeal, brown sugar, melted butter, and cinnamon in a bowl until the mixture becomes crumbly.
Ensure the butter is melted but not hot to achieve the right texture.
Press half of the crumbly mixture into the bottom of a 9-inch square baking pan.
Use a spatula or your hands to evenly press the mixture into the pan.
Spread the diced rhubarb evenly over the base layer.
Ensure the rhubarb is evenly distributed for consistent flavor.
In a saucepan, combine the sugar, cornstarch, water, and vanilla. Cook over medium heat, stirring frequently, until the mixture thickens.
Stir constantly to prevent lumps from forming.
Pour the thickened sauce over the rhubarb in the pan.
Pour the sauce evenly to cover all the rhubarb.
Sprinkle the remaining crumbly mixture over the top.
Gently press the topping to ensure it adheres well.
Bake in a preheated oven at 350°F (175°C) for one hour.
Check for a golden-brown topping to ensure it's done.
Allow to cool slightly before cutting into squares and serving.
Serve warm with a dollop of whipped cream or a scoop of ice cream for added indulgence.