Chop chocolate into small pieces and place in a heatproof bowl. Fill a small saucepan halfway with water and place over medium heat. Once water is simmering set bowl over saucepan and melt chocolate, stirring occasionally, until smooth.

Meanwhile, pour strawberries into the bowl of a food processor fitted with the blade attachment. Pulse until they are in fine crumbs.

Crush graham crackers in a sealed plastic bag with a rolling pin. Pour graham cracker crumbs, powdered sugar, and peanut butter into the bowl of a stand mixer fitted with the paddle attachment. Reserve 1 tablespoon of the strawberry crumbs and pour the rest into the mixer bowl. Beat peanut butter mixture until crumbly and combined.

Sprinkle a pinch of reserved strawberry crumbs and a pinch of salt into the bottom of each skull mold. Top with 1 teaspoon of melted chocolate. Keep chocolate over the bowl of hot water when not using to keep it melted.

Using the pastry brush, gently spread the chocolate around until it covers the strawberries and salt, trying not to pick any of it up with the brush. After you've covered the strawberries take any remaining chocolate and brush it up the sides of each mold, you might need to use extra chocolate from the bowl. Keep the coating thin, you want a layer that is about 1/16-inch thick. Set in freezer to harden, about 5 minutes.

Remove from freezer and fill each mold with about 2 teaspoons of the peanut butter mixture. The amount will vary depending on the size of your mold, but you want the skulls to be almost completely full, with a little room left at the top for a thin chocolate layer. Gently press down on the filling to make it firm.

Cover filling with about 1 more teaspoon of chocolate, spreading it to cover filling completely. Smooth out the tops if necessary and freeze until solid, about 20 minutes.

Remove from freezer and flip molds upside down on a clean surface. Tap the mold a couple times on the counter to pop out the skulls. Let sit 10-15 minutes to defrost before serving.