Sea Salt & Caramel Hot Chocolate Bombs

To make caramel powder: Line a rimmed baking sheet with parchment paper (or a silicone mat) and place on a trivet.

Pour sugar into a heavy-bottomed 1-quart saucepan. Heat over medium-low heat until the sugar melts completely. Do not stir, but swirl the pan periodically to make sure all the sugar dissolves. Watch it the entire time it cooks, as the sugar will quickly darken to caramel and can burn. The minute it is fragrant and amber in color, remove the pan from the heat and carefully pour the molten sugar onto the prepared baking sheet. Do not touch the sugar, but tilt the baking sheet as needed to spread the caramel out. Let the caramel cool for 10 minutes to harden.

Use the parchment (or mat) to bend the caramel and crack it into pieces. Transfer the caramel pieces to a food processor and pulse into a fine powder. (The caramel powder can be stored in an airtight container at room temperature for up to 2 days.)

Reserve 1 teaspoon caramel powder for decorating the bombs. Whisk the remaining caramel powder with cocoa in a small bowl. (This will make enough filling for 16 hot chocolate bombs. Store the remaining cocoa-caramel filling in an airtight container, such as a mason jar, for up to 1 month.)

To make hot chocolate bombs: Melt 4 ounces (about 2/3 cup) milk chocolate on the stovetop in a double boiler or in the microwave in 30-second intervals, stirring between each interval.

Pour 1 teaspoon melted chocolate into each of 16 (1-ounce) cups in a silicone hemisphere mold. Use the back of a small spoon, such as a 1/4-teaspoon measuring spoon, to push the melted chocolate up the sides and around the edges of each cup to cover completely. Place the mold on a rimmed baking sheet and freeze until completely hardened, about 5 minutes.

Melt the remaining 2 ounces (1/3 cup) milk chocolate. Working with one cup at a time, pour in 1/2 teaspoon melted chocolate. Spread the chocolate on the sides and edges, coating them well to prevent cracking. Freeze the mold for another 5 minutes.

Line a small rimmed baking sheet with parchment paper and top with an upside-down wire rack, which will keep the bombs from rolling while you're filling them. Remove the chocolate shells from the mold by gently peeling the silicone away from the edges of the chocolate with your thumbs and pushing from the bottom of the mold with your index fingers.

Heat a microwave-safe plate in the microwave for about 30 seconds, just until warm. Place 1 chocolate shell, open-side down, on the plate, and melt the edges until flat. Carefully spoon 1/2 teaspoon cocoa-caramel filling and a pinch of flaky sea salt into the shell. Place the shell on the rack to hold it upright, then repeat the melting process with a second shell. Fill that half with marshmallow bits (about 3/4 teaspoon).

Carefully press the two halves together. (Don't worry; the contents will stay in place.) Use your finger to spread the melted chocolate around the seam of the bomb to seal it closed. Repeat until all the bombs are filled and sealed.

Melt semisweet chocolate and place in a small zip-top sandwich bag. Snip a small corner off the bag, then drizzle the chocolate over the bombs. Sprinkle the reserved caramel powder and more flaky sea salt, if desired, over the bombs to decorate. (Refrigerate the hot chocolate bombs in an airtight container for up to 1 month. Bring to room temperature before serving.)

To serve: Heat milk in a saucepan over medium-low heat just until steaming hot. Place a hot chocolate bomb in a mug and pour 3/4 cup steaming milk over the bomb. Stir well until the chocolate is melted and fully dissolved. Serve with additional marshmallow bits, if desired.