Preheat the oven to 350°F and coat a 9×13 baking dish with nonstick spray, covering both the bottom and sides.

Add the pretzels to a food processor and pulse until they are broken into small pieces without turning into crumbs. Add ¾ cup of sugar and the melted butter, then pulse a few more times just until combined. Press the mixture evenly into the bottom of the prepared pan.

Bake the pretzel crust for 10 minutes, then remove it from the oven and let it cool completely.

In a large mixing bowl, beat the cream cheese with the remaining ¾ cup of sugar and the vanilla until smooth and fully combined. Gently fold in the Cool Whip until evenly incorporated.

Spread the cream cheese mixture over the cooled crust, making sure to push it all the way to the edges to create a seal that keeps the gelatin from soaking into the pretzels.

Drain the mandarin oranges and reserve 2 cups of the liquid. If the oranges are packed in syrup, use 2 cups of cold water instead. Chill the liquid by adding ice cubes or placing it in the refrigerator.

In a medium bowl, stir the gelatin into 2 cups of boiling water until completely dissolved. Add the chilled mandarin liquid, then fold in the mandarin oranges. Refrigerate for about 30 minutes, just until the mixture begins to thicken but is not fully set.

Slowly pour the gelatin and mandarin mixture over the cream cheese layer. Cover and refrigerate for about 2 hours, or until fully set. Cut into squares before serving.