Step 1

Make the crisp topping by mixing the brown sugar, ground ginger, star anise, and flour together in a small bowl. Grate the cold butter into the bowl. Using either your fingers or a pastry cutter, work the butter into the sugar mixture until it has the texture of wet sand. Mix in the oats. Keep mixture chilled until needed later.

Step 2

Preheat oven to 350°F. Grease an 9" pie pan generously with butter. Set aside.

Step 3

Make the filling by mixing together the rhubarb, granulated sugar, salt, ginger, lemon juice, and arrowroot starch until thoroughly combined. Spread filling evenly into the buttered pie pan.

Step 4

Take the crumble topping out of the refrigerator and spread evenly over the rhubarb filling.

Step 5

Bake until filling is bubbly, and the crumble topping is a dark golden brown. Approximately 35-40 minutes.

Step 6

Let cool at least 20 minutes before serving.