In a medium saucepan, combine tomatoes, sugar, cider vinegar, and orange zest. Cook uncovered, over medium heat, occasionally stirring, until the mixture becomes thick, about 45 minutes. If you pull a spoon through the jam, the jam will stay apart and not close together. Remove from heat. Allow to cool completely before using.

Preheat the oven to 350F

In the bowl of an electric mixer using the paddle attachment combine butter, sugar, vanilla extract, and salt and mix on medium speed until light and fluffy; about 5 minutes. Remove from the mixer, and using a rubber spatula, stir in the flour and ground hazelnuts until thoroughly combined. The dough will look slightly stiff. Using a small ice cream scoop, scoop about 1 tablespoon of dough and make a small round. Place on two parchment-lined sheet trays, and using your thumb or index finger, press down in the center of the dough to make a large circle. Place about 1 ½ teaspoons of tomato jam in the circle. You want the circle to be filled without overflowing. Place the sheet trays in the oven and bake for about 15 minutes or until the cookies are lightly golden and firm to the touch. Remove from oven and allow to cool completely before serving. Sprinkle with powdered sugar, if desired.