Preheat your oven to 350°F (175°C). In a mixing bowl, combine melted butter with 1 tablespoon of sugar, then stir in finely crushed pretzels until evenly coated. Press this mixture firmly into the bottom of an ungreased 13x9-inch baking pan. Bake for 10 minutes, or until lightly golden, then remove from the oven and let it cool completely.

In a large mixing bowl, combine 2 cups of boiling water with the orange gelatin powder, stirring vigorously for about 2 minutes until fully dissolved. Next, carefully fold in the drained crushed pineapple and mandarin oranges. Allow the mixture to cool slightly, then refrigerate for about 30 minutes, or until it begins to set but is not fully firm.

While the gelatin mixture is chilling, beat 8 ounces of cream cheese and the remaining sugar in a mixing bowl until smooth and creamy, about 3-5 minutes. Gently fold in the whipped topping until well combined, being careful not to deflate the mixture.

Once the pretzel crust is completely cooled, spread the cream cheese mixture evenly over the crust. Make sure to cover the edges thoroughly to prevent the crust from becoming soggy. Then, gently spoon the partially set gelatin mixture over the cream layer, spreading it evenly.

Cover the assembled Orange Gelatin Pretzel Salad with plastic wrap and return it to the refrigerator. Let it chill for 2 to 4 hours, or until the gelatin is fully set.

When ready to serve, cut the salad into squares or rectangles. Optionally, top with additional whipped topping and mandarin orange slices.