rhubarb crisp recipe

#### Ingredients: ##### For the Filling: - **4 cups fresh rhubarb** (cut into 1/2-inch pieces) - **1 cup granulated sugar** - **1 tablespoon all-purpose flour** - **1 teaspoon vanilla extract** ##### For the Topping: - **1 cup old-fashioned rolled oats** - **1 cup all-purpose flour** - **1 cup brown sugar** (packed) - **1/2 cup unsalted butter** (melted) - **1/2 teaspoon ground cinnamon** - **1/4 teaspoon salt**