How to Make It
Preheat the oven to 350°. Line two baking sheets with parchment paper. In a small bowl, whisk the flours with the cardamom and salt. In a medium bowl, using an electric mixer, beat the butter with the sugar at medium speed until light and fluffy, about 3 minutes. Beat in the egg and vanilla. At low speed, beat in the dry ingredients. Gather up the dough and knead a few times to form it into a ball.
Using a small ice cream scoop or a tablespoon measure, portion the dough into 36 rolled balls. Arrange the balls on the prepared baking sheets about 1 inch apart. Using the back of a teaspoon, make an indentation in the center of each ball. Bake the cookies for 10 minutes, until slightly firm. Remove the baking sheets from the oven and press the indentations again. Return the cookies to the oven and bake for 7 to 8 minutes longer, until lightly golden and dry but not hard. Transfer the cookies to racks to cool completely. Fill the thumbprints with jam and serve.