Preheat oven to 350

Chop rhubarb into ½-3/4" pieces.

Places rhubarb in a gallon size bag, add corn starch and toss until well coated.

In a bowl combine flour, brown sugar, oats and cinnamon and toss to combine.

Add melted butter and vanilla to oat mixture and stir to make a crumbly mixture.

Place half the mixture into an 8x8 baking dish and press it firmly into the bottom of the pan.

Add rhubarb to the baking dish and pour the Rumchata over the rhubarb.

Place the rest of the oat mixture on top of the rhubarb but don't pack it down.

Bake for 45 minutes or until top is browned. Serve warm with ice cream on the side.