Chocolate Thumbprint Cookies

Position rack in the center of the oven; preheat to 375 degrees F. Line a large baking sheet with parchment paper or a silicone baking mat.

Whisk all-purpose flour, whole-wheat flour, baking soda and salt in a medium bowl until well combined. Grind walnuts in a food processor until they resemble coarse meal.

Beat butter, oil, granulated sugar and brown sugar in a large bowl with an electric mixer until almost creamy--the mixture may still be a little grainy. Beat in egg and vanilla; scrape down the sides and beat in melted chocolate and the ground nuts. Stir in the dry ingredients with a wooden spoon until just incorporated.

Roll 1 tablespoon dough into a ball, place on the prepared baking sheet and flatten slightly until it looks like a deflated basketball. Continue with the remaining dough, spacing the cookies 2 inches apart.

Bake the cookies for 6 minutes. Remove from the oven and gently press your thumb or the end of a wooden spoon in the center of each cookie. Place 1/2 teaspoon jam in each indentation. Bake until the jam is melted and the cookie is set but still a little soft, 8 to 10 minutes more. Cool on the pan for 2 minutes, then transfer to a wire rack to cool completely. Let the pan cool for a few minutes before baking another batch.

Enhancements

Use any flavor jam you want, just don't use preserves (the pieces of fruit may be too large) or jelly (it will melt too quickly and run).