Combine flour, sugar, oats, salt, and nuts in a medium bowl. Add melted butter and combine with hands until mixture is coarse and crumbly.
For mini tarts, drop a generous teaspoon of mixture into each hole; for cupcake-sized tarts, line a tin with foil cupcake liners and drop a generous tablespoon into each liner. Press down.
Use leftover mixture to sprinkle on tarts before baking.
Sweetened whipped cream
Combine pumpkin, cream cheese, sugar, and vanilla with an electric mixer until smooth. Add eggs and seasoning and mix completely. Spoon into prepared crust (1 Tbsp. for minis, 2 generous Tbsp. for regulars) and sprinkle with reserved topping.
Bake at 350; for mini tarts, bake for about 15 minutes. For the regular tarts, bake closer to 20. If you'd like the crumb topping a little darker, you can turn the broiler on for a few minutes, but you have to keep a close eye on them because they will literally burn in a few seconds.
GLUTEN FREE NOTE: I would suggest preparing the filling before mixing the crust. When I made these, it seemed like the crust dried out a bit while I made the filling. If you make the filling first, you can just remix it when you want to spoon it in.
*Did you know that making your whipped cream with powdered sugar instead of normal sugar makes it softer and sweeter? Try it!