How to Make It
Beat butter and powdered sugar at medium speed with a heavy-duty electric stand mixer 2 to 3 minutes or until pale and fluffy. Add egg yolk and vanilla, beating until blended.
Stir together flour and next 4 ingredients in a small bowl. Gradually add flour mixture to butter mixture, beating at low speed until blended after each addition.
Turn dough out onto a lightly floured surface; knead 3 to 4 times. Shape dough into a 1-inch-thick disk. Wrap tightly in plastic wrap, and chill 2 to 24 hours.
Preheat oven to 350°. Stir together pecans and granulated sugar in a small bowl. Shape chilled dough into 1-inch balls. Lightly beat egg white. Dip each ball into egg white; dredge in pecan mixture. Place 1 inch apart on a parchment paper-lined baking sheet. Press thumb into each ball, forming an indentation.
Bake at 350° for 10 minutes. Remove from oven, and, using back of a spoon, press indentations again. Spoon about 1/2 tsp. Tomato Jam into each indentation. Bake 8 to 10 more minutes or until golden brown. Cool on baking sheets 5 minutes; transfer to a wire rack, and cool completely. Store in an airtight container up to 4 days.