Poppy Seed Thumbprints

Position rack in center of oven; preheat to 300°F.

Whisk whole-wheat flour, all-purpose flour, poppy seeds and salt in a large bowl. Beat butter, oil and sugar in another large bowl with an electric mixer on high speed until creamy. Add egg, lemon zest and vanilla; beat to combine. Stir in the dry ingredients with a spoon until just combined.

Form tablespoonfuls of dough into balls and place on an ungreased baking sheet, spacing the cookies about 2 inches apart. Gently press the tip of your thumb or finger in the center of each cookie. Place 1/2 teaspoon preserves in each indentation.

Bake the cookies, one batch at a time, until the edges are lightly golden, 28 to 30 minutes. Immediately transfer to a wire rack to cool completely.