I wondered: How could we get the flavor of doughnuts inside a chocolate truffle? In a trial-and-error process, I tried to infuse doughnuts into the cream for the ganache, but they disintegrated into the cream. Then I thought: Let's embrace this, and simply puree the doughnuts in the cream. And that actually proved to be a wonderful thing because it gives the ganache a wonderful texture in addition to the great doughnut flavor. The result is a really creamy truffle that tastes like a well-made doughnuts.
In a small saucepan, combine the heavy cream, doughnuts, sugar, salt, and cinnamon. Bring to a simmer over medium-low heat, stirring constantly. Be careful not to scorch the mixture: If the paste begins to stick to the bottom of the pot, reduce the heat. Using an immersion blender, blend the mixture until pureed. Remove from heat and add the milk chocolate. Using a wooden spoon, stir in the chocolate until melted and smooth. Use the immersion blender again, as needed to create a smooth ganache. Allow to cool completely; the ganache should be smooth, but thick like peanut butter.
Transfer the ganache to a plastic piping bag or large zip-top bag. Cut a small ½-inch tip in the piping bag or zip-top bag and pipe the filling directly into the truffle shells, all the way to the top. (If not using truffle shells, pipe the ganache in ¾-inch kisses onto parchment-lined baking sheets.)
Freeze the truffles for about 1 hour.
In a medium saucepan, bring 1 to 2 inches water to a simmer over medium heat. Remove from heat. In a metal bowl with a diameter slightly larger than the saucepan (the bowl should nestle comfortably in the pot without the bottom touching the water), combine the chocolate and oil. Nest bowl inside pot. Melt the milk chocolate, stirring with a rubber spatula. Don’t let the chocolate get too hot; it should be between 95 and 100°F. (While working with the truffles, if your chocolate begins to get too cold, place the bowl over the hot water bath and stir until it is fluid again—but not too hot! You may have to do this a few times, so keep the pot on low heat while working with the chocolate.)
Meanwhile, in a large bowl, whisk together the confectioners’ sugar, cocoa powder and cinnamon. Set aside.
Once the chocolate is melted, you will need someone to help you coat the truffles. I suggest using disposable gloves to reduce the mess. Dip the palms of your gloved hands in the melted milk chocolate and rub them to get the gloves completely coated on the palms. If you’ve piped the truffles into the truffle cups, pick up one truffle (or up to three at a time) and roll between your palms like you are making clay balls to coat it with chocolate. (If not using truffle shells, simply roll the chocolate kisses in your gloved hands into balls.)
Drop each truffle into the bowl with the confectioners’ sugar mixture. Have your helper toss the truffles in the sugar to coat them completely, then transfer to a sieve and gently shake to remove any excess sugar. Repeat to coat all of the truffles.
Store the truffles in an airtight container at room temperature for up to 2 weeks, or refrigerate for up to 6 weeks.