Make the caramel sauce ahead of time, so it has time to cool and thicken. You do not want it hot or warm when spooning into the baked thumbprints.

Preheat oven to 325°F (163°C). Line large baking sheets with parchment paper or silicone baking mats. (Always recommended for cookies.) Set aside.

Place the coconut in a food processor and pulse until finely chopped (about 15 quick pulses). If you don’t have a food processor, spread the coconut out on a cutting board and give it all a rough chop.

In a large bowl using a hand mixer or a stand mixer fitted with a whisk attachment, beat the egg, egg whites, sugar, salt, and vanilla together on medium-high speed until the sugar is dissolved and the mixture is frothy, about 1–2 minutes. Fold in the coconut until completely combined.

Using a medium cookie scoop or a spoon, scoop 1.5 Tablespoons (about 30g) of the mixture and arrange 2 inches apart on prepared baking sheets. With your thumb, finger, or a small measuring spoon, press into the center of each macaroon to make an indent.

Bake until lightly golden and set around the edges, 20–24 minutes. Keep a close eye on them after around 18 minutes. You want to take them out of the oven when they’re starting to turn a toasty, golden color but are still mostly white; over-baking will dry out your coconut macaroons.

Cool for at least 10 minutes on the baking sheet set on a cooling rack.

Spoon salted caramel into the middles of the macaroons (use however much will fit—about 1/2–1 teaspoon each).

You can melt it in a double boiler or use the microwave. If using the microwave: place the chocolate in a medium heat-proof bowl or glass liquid measuring cup. Microwave for 20-second increments, stirring after each, until chocolate is completely melted and smooth. Drizzle chocolate over the cooled macaroons. Sprinkle with flaky sea salt, if desired. Allow chocolate and caramel to set, either at room temperature or in the refrigerator (to speed it up).

Cover and store macaroons at room temperature for up to 3 days or in the refrigerator for up to 1 week.