Bring the cream to a boil in a saucepan, then turn off the heat. The cream needs to be warm when it’s added to the caramel; if used cold, the difference in temperature will cause it to bubble vigorously.

In a bowl that's large enough to hold all of the ingredients, place bittersweet and milk chocolate, then set aside.

Make the caramel (check out my guide about caramel to learn more): In a medium heavy-bottomed saucepan (large enough to coat the surface with an even thin layer of sugar), heat sugar over medium heat. The caramel will usually start to brown at the edges first. In that case, gently push the liquefied sugar towards the middle of the pan using a heatproof utensil such as a whisk, spatula, or wooden spoon. Mix the sugar occasionally, or swirl and shake the pan to cook evenly and prevent it from burning, but don’t over mix as this encourages clumping. If clumps form, that’s ok; they will eventually melt.

Once all the sugar has melted, pay careful attention and watch the pan, swirling it occasionally until the caramel turns a deep amber color. Add the butter very carefully, keeping your face away from the pan (mixture will bubble up!), and whisk vigorously until butter has melted and fully combined. Carefully add salt and cream in a steady stream and keep whisking until combined, then remove pan from heat.

Pour about one-third of the caramel into the center of the chocolate mixture and, working with the wooden spoon, gently stir the creamy caramel into the chocolate in ever-widening concentric circles. When the ganache is smooth, add half of the remaining caramel, blending it into the chocolate in circles, then finish with the rest of the caramel in the same manner and mix until completely smooth. Cover bowl with plastic wrap, place in the refrigerator and chill for at least 4 hours.

When you are ready to shape the truffles, spoon a generous amount of cocoa powder into a bowl, and set out a baking sheet lined with parchment or waxed paper. Remove the truffle mixture from the refrigerator, and for each truffle, scoop up the ganache (I measure them the size of 1 tablespoon exactly using this ice cream scoop). Drop each truffle in the bowl of cocoa powder and toss until well coated, then place on the paper-lined pan.

Store in the refrigerator in an airtight container for up to 3 days.