Preheat the oven to 175 ° C. Line two baking sheets with parchment paper and have them ready.
In a large bowl, beat the butter and peanut butter until frothy, stir in the sugar and vanilla extract, egg and milk for a minute. Next, briefly mix in the salt, baking powder, flour and pretzel crumbs, then fold in the chocolate pieces.
Place small piles of dough on the baking sheet with a tablespoon and press in a little cross-shaped with a fork. Sprinkle each cookie with a little fleur de sel.
Place the trays in the oven for approx. 10 - 12 minutes and bake.