1. Preheat oven to 375°F. In a medium bowl, whisk together flour and salt; set aside. In a large bowl, beat butter, granulated sugar and brown sugar with an electric mixer on medium until smooth. Beat in egg yolks and vanilla until combined. Slowly beat in flour mixture until combined. Let dough stand at room temperature for 30 minutes.
2. In a shallow bowl, place chopped pistachios. Roll dough into 1-inch balls; roll balls in pistachios to coat. Place balls 2 inches apart on two large ungreased cookie sheets. Using your index finger, make a round indentation in the top center of each ball. Avoid pushing more than halfway through.
3. Bake, one cookie sheet at a time, for 8 to 10 minutes or until bottoms are golden brown, rotating cookie sheet halfway through. Remove from oven. Reshape center indentations, if necessary. Cool on cookie sheet for 5 minutes. Transfer cookies to wire racks and cool completely.
4. Just before serving, spoon preserves into center of each cookie.

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To store: Place cookies without the preserves between sheets of waxed or parchment paper in an airtight container; store at room temperature up to 3 days or in the freezer up to 1 month. To serve, thaw cookies, if frozen. Fill with preserves as directed.