In a large bowl, mix together butter and brown sugar until it becomes a sand-like texture. Add eggs and beat with electric mixer. Add whipping cream and vanilla extract; mix until smooth. Add in flour, salt, cinnamon, allspice, and nutmeg.
Scoop out the inside of the sweet potatoes and transfer them to a medium bowl and mash. Once mashed, add potatoes into the flour mixture and blend with electric mixer.
Roll out the dough and with tartlet pans, divide the dough into 12 (4-inch) rings. Spray the tartlet pans with nonstick cooking spray and insert dough. Cut off excess dough with a knife.
With an ice cream scooper, scoop out potato mixture; about 1/4 cup each and place into tartlet pans.
Bake for 30 minutes. Once cooled, garnish with whipped cream.