Prep a small mixing bowl by adding the cubed butter to it, along with a fine mesh sieve. Set aside.
Add the sugar to a small saucepan, then zest the blood orange into the pan. Use your fingers to rub the zest into the sugar.
Add in the blood orange juice, egg yolks, and salt.
Set the saucepan over medium heat, stirring constantly (this can be slowly - we just need constant movement happening!)
Continue to stir the curd until it thickens and reaches a temperature of at least 170°F / 76°C (This took me about 3-5 minutes.)
Remove the curd from the heat and pass it through the fine mesh sieve, over the butter. Mix the curd and the butter together until the butter has melted and the mixture is smooth.
The curd will have lost it's bright red color but don't be alarmed - it's unfortunate but just naturally happens with the cooking process. Transfer the curd to the fridge to chill until you're ready to assemble the cookies.
Once the cookies have chilled, preheat the oven to 350°F / 175°C. Line a cookie sheet with parchment paper or with a silicone baking mat.
Use a 3 tbsp. cookie scoop to dish out the cookies onto the prepared cookie sheet, evenly spacing them apart to allow room for spreading.
Bake for 10-12 minutes, until the sides of the cookies just start to turn golden brown, and the top of the cookies looks just slightly wet. Let the cookies rest on the hot baking sheet for at least 5 minutes before transferring them to a wire rack to cool.
Allow the cookies to come to room temperature before frosting them.