Make the filling: In a bowl, mix peanut butter with powdered sugar (start with 1/2 cup per 1 cup peanut butter), 1 teaspoon vanilla, and 1–2 tablespoons softened butter until thick but spreadable.
Assemble the sandwiches: Lay pretzels on a parchment-lined tray. Spoon or pipe a small mound of filling onto half the pretzels.
Top with remaining pretzels to make sandwiches and gently press.
Chill to firm: Freeze the tray for 15–20 minutes so the filling sets and dipping is easier.
Melt the chocolate: Microwave chocolate with a teaspoon of coconut oil in 20–30 second bursts, stirring between each, until smooth. Or melt over a double boiler.
Dip and decorate: Dip each pretzel bite halfway into the chocolate. Let excess drip off, place back on the tray, and sprinkle with flaky salt before the chocolate sets.
Set and store: Chill 10–15 minutes until the chocolate is firm.
Transfer to an airtight container.