Preheat the oven to 350°F.
Grease the inside of a 9 x 13-inch baking pan.
To make the crust, add the pretzels, melted butter, and sugar to a large mixing bowl. Stir until well-combined.
Transfer the mixture to the baking pan, then press it evenly into the bottom.
Bake the crust for 10 to 12 minutes, until it darkens just slightly.
Place the crust on a cooling rack and let it cool completely.
To make the filling, place all ingredients into a blender or food processor, and blend until smooth, stopping to scrape down the inside of the pitcher or bowl as needed.
Pour the filling over the pretzel crust and use a spatula to smooth out the top.
Cover the baking dish and place it in the fridge to chill for at least 4 hours, until the filling is completely set.
You can make the topping once the filling is set (don't make it too soon or it will start to set). Whisk 1 cup of the juice and agar together in a small saucepan and place it over medium heat. Bring the juice to a boil, reduce the heat and let it simmer for a full 2 minutes, whisking frequently.
Remove the pot from the heat and whisk in the remaining cup of juice. Let the mixture cool until it's just lukewarm. Check on it frequently to make sure it hasn't started to set. If you notice it setting, move on to the next step right away.
Once the juice has cooled to lukewarm, pour it into a large bowl and stir in the strawberries. Work quickly from this point, as the berries will cool down the juice and can start the setting process, particularly if they've been in the fridge.
Pour the topping over the filling, gently smoothing it out and repositioning the berries as needed.
Cover the dish and chill until the topping is set, at least one hour.
Slice, serve and enjoy!