Pass the berries through a food mill fitted with a fine disk or force them through a through a fine sieve, mashing with a wooden spoon, into a medium bowl. You'll have about 1/2 cup raspberry puree; set it aside and discard the contents of the strainer.
Put the chopped chocolate in a medium bowl.
In a small saucepan, heat the cream, just until boiling.
Pour the hot cream over the chopped chocolate; whisk to blend.
Stir in the raspberry puree and the salt.
Refrigerate the mixture until completely chilled, about 1 hour.
Pour the cocoa powder onto a plate.
With a melon-baller or spoon, scoop the chocolate-raspberry mixture and shape it into 1-inch balls.
If the truffles are very soft, put them on a baking sheet and refrigerate briefly to firm.
Roll the shaped truffles in the cocoa, coating them thoroughly.
If sealed and refrigerated, these truffles will keep for about 1 week.