1/2 cup apple cider vinegar
1/2 cup plus 1 teaspoon granulated sugar, divided
1 Granny Smith apple, cored, peeled and cut in 1/2-inch cubes
1/4 teaspoon ground allspice
Salt
2 cups all-purpose flour
1 1/2 cups shredded sharp Cheddar cheese
1 teaspoon freshly ground black pepper
1/2 teaspoon baking powder
1 pinch ground red (cayenne) pepper
1 cup (2 sticks) cold unsalted butter
Sour cream
1/2 pound thinly sliced good-quality ham, torn in 1-by-2-inch pieces
Flat-leaf parsley, for garnish
First, make the jam. Bring vinegar and 1/2 cup sugar to a boil in medium saucepan over medium heat. Stir to dissolve sugar, then add apple, allspice and a pinch of salt. Cook until mixture gels, about 20 minutes. Transfer to a small bowl; refrigerate until ready to use. (Makes 1 cup jam).
Then, make the shortbread. Put flour, Cheddar, 1 1/2 teaspoons salt, pepper, 1 teaspoon sugar, baking powder and cayenne into bowl of a food processor fitted with a steel blade. Pulse a few times to combine. Cut butter into small bits; add to flour. Pulse just until dough begins to come together.
Transfer dough to a floured surface, and knead until all butter is combined. Divide dough in half; roll each piece into a log about 1 1/2 to 2 inches in diameter. Refrigerate for 20 minutes. Preheat oven to 350 degrees.
Slice each log into 1/4-inch rounds. Place rounds on a baking sheet; bake in top half of oven until browned, 15 to 20 minutes. Remove and let cool 10 minutes before transferring to a rack to cool completely.
To assemble, put a small dollop of sour cream on each shortbread. Fold a piece of ham and place it on top of sour cream. Top with 2 teaspoons of Apple Jam, and garnish with a parsley leaf.