• In a large bowl, whisk together the flour, cream of tartar, baking soda and salt. Set aside.
  2 1/4 cups (281 grams) flour, 1/2 teaspoon cream of tartar, 1/2 teaspoon baking soda, 1/2 teaspoon salt
• In another large mixing bowl with an electric hand mixer, beat together the butter, oil, granulated sugar and powdered sugar until well blended.
  1/2 cup (113 grams) unsalted butter, 1/2 cup (99 grams) vegetable oil, 1/2 cup (100 grams) granulated sugar, 1/2 cup (60 grams) powdered sugar
• Add the egg, lemon zest, and lemon extract and beat until fully incorporated.
  1 large egg, 2 tablespoons lemon zest, 1 teaspoon lemon extract
• Gradually beat in the dry mixture to the wet mixture, mixing just until combined. Be careful not to overmix; the dough should be light and fluffy. It’ll be too wet to form into balls at this point.
• Chill for at least 6 hours. Overnight or 2-3 days also works.
• Line a baking sheet with a piece of parchment paper. Preheat the oven to 375 °F.
• Place the raw sugar in a small bowl.
  3 tablespoons raw sugar
• Roll the dough into 24 30-gram balls.
• Roll into the raw sugar and place the balls on the prepared baking sheet. Don't press down!
• Bake for 8-12 minutes or until the top center no longer looks wet.
• Remove from the oven and use the back of a 1-teaspoon measuring spoon to create an indentation. I pressed down almost all the way (but don't break through the cookie!).
• Fill with about 1/2 to 3/4 teaspoon jam.
  3-4 tablespoons raspberry jam
• Put back in the oven and bake for another 4-7 minutes. They'll have crackled a bit.
• Remove from the oven and let cool completely on the baking sheet, about 2 hours.
• Mix the powdered sugar with the lemon extract and gradually add 1-2 tablespoons of milk until you achieve a drizzling consistency.
  1/2 cup (60 grams) powdered sugar, 1/4 teaspoon lemon extract, 1-2 tablespoons milk
• Pipe over the cookies. Let the icing harden for about 2 hours or until firm. If you're in a hurry, you can refrigerate them.

How to store:

• After cooling, these raspberry thumbprint cookies can be stored in an airtight container at room temperature for up to 4 days. If you prefer to keep them for longer, store them in the refrigerator for up to a week. I prefer them refrigerated as they're chewier when cold. They can also be frozen for up to 3 months.