Line a baking sheet with parchment or a silicone mat.

In a small bowl, whisk together all purpose flour, ground cardamom, ground cinnamon, and kosher salt.

In a large mixing bowl or the bowl of a stand mixer, whip butter on high speed until smooth and creamy.

Add the granulated sugar and mix until creamy and well combined.

Add the egg, vanilla extract, orange zest, and orange oil, and mix until well combined.

Add dry ingredients and mix on medium speed, scraping down sides of bowl as necessary, until a firm dough forms.

With a melon baller or cookie scoop, divide dough into 24 portions. Use your hands to roll each portion into a smooth ball.

Arrange on prepared tray. Refrigerate 30 minutes. (If your tray doesn’t fit in the refrigerator, you can refrigerate the balls on a parchment-lined plate.) Meanwhile, preheat oven to 350° F / 176° C.

Roll each ball in granulated sugar.

With your thumb, create a deep indentation in the top of each ball.

Bake in preheated oven for 13-14 minutes, or until very lightly golden brown around the edges. Do not overbake.

Working quickly but carefully, use a 1/2 teaspoon to re-indent the top of each cookie. (Use a twisting motion and don’t press too hard, or the cookies will crack.)

Cool on tray for 5 minutes, then transfer to a wire rack to cool completely.

Fill each cookie with 1/2 teaspoon of orange curd. Garnish with orange zest, if desired.

Serve immediately. Store leftover orange curd thumbprint cookies in the refrigerator for up to 1 day.