Line an 8 inch (20 cm) square baking tin with baking paper.
Roughly crush 75g (2 cups) of the mini pretzels, either by pulsing in a food processor, or by putting them into a sandwich bag and crushing them with a rolling pin.
75 g (2 cups) salted mini pretzels
Combine the peanut butter, butter and sugars in a bowl until smooth, then stir in the crushed pretzels. Press this mixture evenly into the lined pan, and chill for 20 minutes.
270 g (1 cup) creamy peanut butter, 2 tbsp unsalted butter or vegan butter, 50 g (1/4 cup packed) light brown sugar, 75 g (1/2 cup + 2 tbsp) icing sugar (powdered sugar)
Meanwhile, melt the chocolate (see notes) and pour over the chilled peanut butter mixture, using a rubber spatula to spread it evenly and smooth it out. Tap the pan against a hard surface to even out the chocolate a bit more.
250 g (1 1/2 cups) milk chocolate or dark chocolate
Place 25 mini pretzels evenly in a grid pattern on top of the chocolate (they'll be your guide for cutting the bars). Leave at room temperature until the chocolate has set. If you're pressed for time, pop the tin into the freezer for 10-15 minutes so the chocolate can set quicker.
75 g (2 cups) salted mini pretzels
Run a hot butter knife around the inside edge of the pan to release the bars. Use the baking paper to lift the bars out of the tin. Use a hot, sharp knife, to cut into 25 squares.
Store in an airtight container for up to 2 weeks. You can keep them at room temp if your home is cool or in the fridge if they're getting a bit melty.