Preheat your oven to 350° F.
In a medium bowl whisk together the flour, granulated sugar, brown sugar, cinnamon, oats and salt.
Add the melted butter and stir with a fork to combine. The mixture should look cumbly.
Spread the mixture on a parchment lined baking sheet.
Balke for 10-12 minutes. The crumble should be golden brown. It will not be crisp when removed from the oven, but it will crisp up as it cools.
Once completely cool break up the crumbles and store in an airtight container until ready to use.