Prepare the Pan: Line a quarter sheet pan with a sheet of parchment paper, ensuring it lays flat against the bottom and sides.
Toast the Nuts: Preheat your oven to 325°F (165°C). Spread the pistachios on a small baking tray and toast for 5-7 minutes until fragrant. Let them cool completely, then roughly chop.
Whip the Yogurt Base: In a medium bowl, combine the Greek yogurt, agave nectar, lime zest, vanilla extract, and ground cardamom. Stir with a spatula until the mixture is smooth, creamy, and evenly blended.
Assemble the Bark: Pour the yogurt mixture onto the prepared sheet pan. Use the spatula to spread it into a thin, even layer, approximately ¼-inch (⅔ cm) thick.
Create the Swirl: Drop small dollops of the strawberry-rhubarb preserves randomly over the yogurt. Drag the tip of a skewer or a spoon through the dollops to create an elegant, marbled pattern.
Add the Crunch: Evenly sprinkle the chopped, toasted pistachios over the entire surface of the swirled yogurt.
Freeze Until Firm: Carefully transfer the pan to the freezer. Let it freeze for at least 2 hours and 30 minutes, or until the bark is completely solid and firm to the touch.
Portion and Serve: Once frozen, lift the parchment paper to remove the bark from the pan. Break it apart into 24 rustic pieces. Serve immediately.
