In a medium bowl, cream together butter and sugars.
Add egg and vanilla to butter mixture and combine until smooth.
In a small bowl, mix flour and salt.
Add flour mixture to butter and combine until all the flour is incorporated. Cover and place in fridge for 30 minutes, or until chilled through.
Preheat oven to 350 degrees F. Line baking sheet with parchment paper.
Once dough has chilled, roll into 1-inch smooth balls and place on baking sheet leaving a little space between balls.
Make an indentation or well in the middle of each ball using your thumb or forefinger. You can smooth out any cracks that form in the cookies using your fingers. Using a teaspoon, fill wells with mincemeat, being careful not to overfill.
Bake 10-12 minutes, until bottoms are slightly golden.
Cool cookies for 5 minutes before removing to a cooling rack.