Combine the flour, sugars, and cinnamon in a bowl, then set aside.
In a small separate bowl, melt the butter, then pour into the flour and sugar mixture. Mix together using a spatula until the flour and sugar are fully incorporated with the butter. The crumble should look like large pieces and stick together.
For the Pears
Slice three pears into ¼" pieces and add to an oven-safe baking dish. Sprinkle a dusting of cinnamon and arrowroot or cornstarch onto the pears and toss to combine.
Sprinkle a generous helping of the crumble on top of the pears, spreading evenly to coat.
Bake the crumble at a 350º oven for 20 minutes. Let cool for 5-10 minutes before serving.
Notes
Prep the crumble ahead of time so that it has enough time to chill and set in the fridge.You have the option to peel your pears if you don't want the skin on.