How to Make It
Preheat oven to 350°F. Place freeze-dried raspberries in a food processor, and process until very finely ground, about 30 seconds. Sift raspberry powder into a small bowl; discard seeds.
Pulse saltines in food processor until very finely crumbled, about 10 times; transfer to a medium bowl, and set aside.
Place 1 teaspoon raspberry powder and egg white in a medium bowl. Beat with an electric mixer on high speed until stiff peaks form, about 1 minute; add to crumbled saltines. Add 2 tablespoons raspberry powder and melted butter to saltine mixture, and stir with a spatula to combine. Press mixture in bottom and up sides of a 13 1/2- x 4 1/4-inch fluted rectangular tart pan with a removable bottom. Bake crust at 350°F until crisp and slightly golden, about 10 minutes. Cool completely on a wire rack, about 40 minutes.
Place whipping cream in a medium bowl. Beat with electric mixer on medium-high speed until stiff peaks form, about 2 minutes. Place chopped chocolate in a medium microwavable bowl. Microwave at high until melted, about 1 minute and 30 seconds, stirring at 30-second intervals. Let chocolate cool 15 minutes, stirring often. Gently fold whipped cream into melted chocolate. Gently fold yogurt into chocolate mixture; pour into cooled crust. Chill 1 hour.
Stir together 1 teaspoon raspberry powder and powdered sugar and in a small bowl. Using a fine wire-mesh strainer, dust powdered sugar mixture over tart. Arrange fresh raspberries on top of tart. Cut into 12 slices.