Start by toasting the coconut in a dry skillet over medium heat, stirring frequently for 3-4 minutes until fragrant and lightly golden. Transfer to a plate to cool—this deepens the flavor and gives the cookies better texture. While the coconut toasts, sift together the flour and salt in a medium bowl, which aerates the flour and ensures even distribution of salt. Measure out all remaining ingredients and set them within reach.

Using an electric mixer, cream the softened butter and sugar together for 1-2 minutes until light and fluffy—this incorporates air and creates a tender cookie texture. Add the vanilla extract and mix until combined. Reduce the mixer to low speed and gradually add the dry ingredient mixture from Step 1, mixing just until a cohesive dough forms. Don't overmix, as this can develop gluten and make the cookies tough.

Shape the dough from Step 2 into a ball, flatten it into a 1-inch thick disk, and wrap it loosely. Refrigerate for at least 30 minutes—this prevents the cookies from spreading too much during baking and makes them easier to handle. While the dough chills, preheat your oven to 350°F and line your baking sheets with parchment paper.

Scoop the chilled dough into 30 portions (about 1½ inches each) and roll each into a smooth ball between your palms. Whisk together the egg and water to create an egg wash. Dip each dough ball into the egg wash, then roll it in the toasted coconut from Step 1, coating all sides evenly. Place the coated cookies on your prepared baking sheets, spacing them about 2 inches apart. I like to leave a small gap between cookies because they spread slightly and we want room to press the thumbprints without them touching.

Using your thumb or the back of a small spoon, gently press an indent into the center of each cookie, being careful not to press all the way through to the bottom. Fill each thumbprint with about ½ teaspoon of jam—don't overfill, as the jam may spread during baking. Bake for 18-20 minutes until the edges are light golden brown and the coconut is toasted. The cookies should still feel slightly soft in the center when you remove them from the oven; they'll continue to firm up as they cool.

Allow the cookies to rest on the baking sheet for 2 minutes to set slightly, then transfer them to a wire cooling rack to cool completely. This brief time on the pan allows them to firm up just enough to move without breaking, while finishing on the rack prevents them from becoming soggy on the bottom.