Add the beer to a small saucepan and cook until it is reduced to about 3 tablespoons. Set aside.
In another saucepan add the heavy cream and heat until steaming, but not boiling. Add the chocolate, but do not mix. Allow to sit for about five minutes.
Add in the beer, vanilla, butter, and salt. Stir gently to completely combine the ingredients.
Allow to cool to room temperature, then chill completely in the refrigerator until solidified - at least one hour, preferably up to four hours.
Lightly coat your hands with oil to prevent the chocolate from sticking to your hands. Place the crushed pretzel into a shallow bowl. Take out a tablespoon and scoop out a portion of the chocolate and quickly roll into a ball. Do not spend too much time handling the chocolate as it will melt. Place the truffles on a baking sheet covered in parchment paper and chill for an hour.
Take out the truffles and put into the bowl of the crushed pretzels to completely coat.
Store the truffles in an airtight container in the refrigerator for up to a week.
Notes
* I used a Southern Tier Creme Brulee Imperial Milk Stout... it is a dessert stout and very delicious on its own and is very nice in these truffles, but feel free to use any kind that appeals to you!