Chocolate Thumbprint Cookies

Position rack in the center of the oven; preheat to 375°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).

Tip: To toast chopped walnuts: Heat a small dry skillet over medium-low heat. Add nuts and cook, stirring, until lightly browned and fragrant, 2 to 3 minutes.

Cooking Tip: To melt chocolate:

Bring 1 inch of water to a simmer in a double boiler set over medium-high heat, then place chocolate in the top pan. (Alternatively, to improvise a double boiler, place chocolate in a heat-safe mixing bowl that fits snugly over a pan with 1 inch of simmering water.) Stir until half the chocolate has melted. Remove the bowl and continue stirring until the chocolate has fully melted. Cool for 5 minutes at room temperature.

Place the chocolate in a microwave-safe bowl and microwave on High for 1 minute. Stir well, then continue microwaving in 30-second increments on High until two-thirds of the chocolate has melted, stirring well after each heating. Remove the bowl and continue stirring until all the chocolate has melted. Cool for 5 minutes at room temperature.