To prepare the Zinfandel-blackberry puree, in a small saucepan, combine the wine, peppercorns and bay leaf. Bring to a simmer and simmer for 5 minutes. Remove from the heat and let stand for at least 1 hour. Strain the mixture through a fine-mesh sieve. 

In a small pot, combine the wine mixture, blackberries and sugar. Bring to a simmer and cook, stirring often, until the wine is almost completely reduced. Immediately transfer the mixture to a blender and puree until smooth. Any extra puree can be stored in the refrigerator for up to 2 weeks.

To prepare the truffles, in a small saucepan, combine the cream and peppercorns. Bring to a simmer and simmer until the cream has reduced by about 1 ounce. Strain the cream through a fine-mesh sieve. 

Place the milk chocolate in a bowl and pour 5 ounces of the cream over the chocolate. Add the Zinfandel-blackberry puree and butter and stir until thoroughly combined. When the mixture is melted and smooth, pour it into a 2-inch-deep pan and refrigerate for at least 4 hours. 

Using a small scoop or a melon baller, scoop out truffles about 1/2 ounce each. Roll each truffle between your palms into a round ball. Refrigerate the truffles until firm.

Line a baking sheet with parchment paper. 

Pour some of the melted dark chocolate on a large, flat plate. Place the cocoa powder in a shallow bowl. Using a fork, roll a truffle in the melted chocolate until completely coated, then immediately place the truffle in the cocoa powder. Gently coat the truffle completely with cocoa powder and transfer to the prepared baking sheet. Repeat with the remaining truffles. Let cool before serving.