Preheat oven to 425°F.
Add 1 Tbsp butter to medium preheated pot. Let butter brown slightly, then add onions and cook until soft. Add sugar and cook to dissolve.
Add cranberries and cook until soft.
Add orange juice and vinegar and simmer on low heat for 10 minutes.
Stir in cornstarch and simmer until mixture thickens. Cool completely.
Cut 8 circles out of pie dough, large enough to fill the cupcake tin with a small amount of overflow, and 8 circles slightly smaller for top.
Scoop cold cranberry filling into pie dough, and cover with smaller pie top. Moisten edges and pinch to seal. (Brush with egg wash for extra golden color.)
Bake mini pies until golden brown, or about 15 minutes.