In a large bowl, mix together flour, sugar, and salt. Add cubes of butter and use your hands to work butter into flour, until a shaggy dough starts to form. Combine water and vinegar and add to dough. Knead dough until it comes together.
Divide dough into two even pieces. Shape each into a disc and wrap in plastic. Chill for an hour while you make the filling.
Peel the grapes by using your fingers to squeeze the fruit out of its skin. Place skins in a bowl and grapes in a medium saucepan. Once grapes are peeled, use a wooden spoon to mash them a bit, then cook on medium heat for about 5 minutes, bringing to a boil and stirring. Let cool slightly.
Press grapes into a bowel through a fine mesh sieve to filter out the seeds. Transfer grape juice back to saucepan and add skins, sugar, cornstarch, lemon juice, and butter. Cook over medium heat, stirring frequently, until grapes thicken. Set aside and let cool completely.
In a medium saucepan, combine pears, sugar, cardamom, lemon juice, cornstarch, and butter. Bring to a boil, and continue to stir until it thickens, about 3-5 minutes. Set aside and let cool completely.
Preheat oven to 400F.
Remove first disc of dough from refrigerator. On a lightly floured surface, roll out dough to about ⅛ inch thickness. Use a 4½ - 5 inch round to cut out 6 circles of dough. You may need to re-roll scraps to get 6. Fit the dough circles into half the slots of a 12 cup muffin tin. Repeat process with second disc of dough. Place in freezer for 10-15 minutes, or until fillings are cool.
Once fillings are cool, scoop concord grape into 6 of the pie crusts and pear cardamom into the other 6. Bake for 20-25 minutes, until filling is bubbly and dough starts to brown. Let cool completely before gently removing mini pies from muffin tin.