Position a rack in the middle of the oven and heat the oven to 325 degrees F. Oil the sides and bottom of a 9 1/2-inch fluted tart pan with a removable bottom. In a food processor, grind the gingersnaps until they're the texture of sand. Transfer to a bowl, add the melted butter, and work it in by squishing the mixture together with your hands. Press into the sides and bottom of the oiled tart pan. Set the pan on a baking sheet and refrigerate for 20 minutes to firm. Bake the tart crust on the baking sheet until fragrant, about 15 minutes, checking and rotating if needed to make the sure the crust doesn't get too dark. Set on a rack to cool.

Meanwhile, pass 1 cup of the berries through a food mill fitted with a fine disk or force them through a fine sieve, mashing with a wooden spoon, into a medium bowl. You'll have about 1/2 cup puree; set it aside and discard the contents of the strainer. Put the chopped chocolate in a medium bowl. 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. Pour the mixture (called a ganache) into the cooled tart shell. Refrigerate until the ganache is fairly firm, about 1 hour. Arrange the remaining raspberries on top of the ganache; they should completely cover the surface. Chill until the ganache is completely firm, about 30 minutes, and serve.

This tart can be made up to a day ahead.