Set out the cream cheese to soften. Preheat oven to 350 degrees F. Crush pretzels with a rolling pin. (To prevent a mess, you can put the pretzels in a gallon Ziploc bag before crushing them.) Leave some pretzels in broken pieces for a more crunchy effect.
Melt butter on the stove or in the microwave. Off the heat, stir in the 3 tablespoons of sugar. Add the crushed pretzels and stir to combine well. Using a spatula, scrape the pretzel mixture into a 9x13 pan and smooth it evenly. Press it into place with your fingers, if needed. Bake the crust for 10 minutes.
When the crust has another five minutes to bake, melt your chocolate in the microwave (use a microwave-safe bowl) by heating it 30 seconds at a time and stirring it occasionally until it is smooth. When the crust is finished baking, spread the melted chocolate onto the crust in an even layer.
In a medium stainless steel bowl, beat the ½ cup whipping cream for a few minutes, until it has the consistency of whipped cream.
In a large bowl, beat the cream cheese, peanut butter, sugar and vanilla until combined. Fold in the whipped cream until it is blended. When the chocolate layer on the crust has cooled, gently add the cream cheese layer to the pan and smooth it evenly. If you will be making your own caramel, refrigerate the pan until the caramel is ready to be added.
To make the caramel, add the half stick of butter, sugar, salt and cream to a medium, heavy-bottomed sauce pan (I used my stainless steel pan.) Stir to combine. Over low heat, melt the ingredients while stirring slowly and gently. Don't rush this part.
When the ingredients are melted, increase the heat to medium-low, stirring, and let the mixture come to a low boil. Stop stirring and let the caramel simmer for seven minutes without touching it. Keep an eye on it, and if it smells like the mixture is burning, lower the heat a bit.
Off the heat, stand back and carefully and gently stir in the vanilla (it will splash) without scraping the sides (to avoid grainy caramel). Set the caramel aside to cool. It should look like thick liquid, rather than soft ball caramel. If it looks like the butter is separating, just stir the caramel over low heat for a couple minutes, until it recombines.
Chop the peanuts. When the caramel has cooled a bit, carefully spread it on top of the cream cheese layer in the dessert pan. (Apply it a section at a time, because the caramel will start to set when it touches the cold cream cheese.) Immediately sprinkle on the peanuts. Cut the dessert into 2 x 2 bars (they are rich) and have a taste before freezing them. To freeze, cover the pan with plastic wrap, then foil, and give the bars a few hours to set.
There is no need to thaw the bars before serving them. Store the bars covered in the freezer.
The bars taste best frozen, but you also might like them just chilled. Full-fat cream cheese works best, but low-fat is okay when the bars are frozen. (The low-fat filling will be too soft when it thaws.) Natural peanut butter is okay to use.