Blood Orange Curd Thumbprint Cookies

For the blood orange curd:
In a medium metal bowl, whisk eggs, sugar, lemon juice, blood orange zest and juice. Set metal bowl over simmering pan of hot water (make a double boiler) and cook mixture, whisking constantly for 8–10 minutes, until thickened.

Add butter and whisk to combine. Be careful not to overcook eggs. Remove from heat and strain through a very fine mesh sieve. Cover with plastic wrap and let cool to room temperature (it will thicken even more) before you fill cookies with it. Keep in an airtight container in fridge for up to 1 week.

For the cookies:
In bowl of a stand mixer with paddle attachment, beat butter on high until creamy, about 2 minutes. Add sugar and vanilla extract. Beat on medium until combined. Scrape down sides of bowl if needed.

Add flour and salt, and beat on low, until it is slowly incorporated and dough is formed. Wrap dough with plastic wrap and chill for 1 hour.

Take out of the fridge and let dough soften just a little for 5–10 minutes. Scrape about 1 tablespoon cookie dough and roll into balls. Line a baking sheet with parchment paper (or Silpat) and place dough balls on it, leaving about 2 inches in between. Using your thumb (or a ½-teaspoon measuring spoon), make an indentation. Chill cookies for at least 30 more minutes.

Preheat oven to 350ºF (177ºC). Bake cookies for 14–15 minutes, until very lightly browned. If for some reason thumbprint indentations have puffed up, very carefully press with back of a measuring spoon (or a similar object) to re-shape. Let cookies cool on baking sheet for 10 minutes, then transfer to cooling rack and let them cool completely.

Fill each cookie with about 1 teaspoon blood orange curd. Keep in an airtight container in fridge for up to 5 days.