Combine the chocolate chips, the milk, and the butter in a medium size glass bowl and heat in the microwave for 90 seconds. Stir to combine and heat another 15 seconds. Stir and heat an additional 15 seconds, only if needed. There will still be a few pieces of unmelted chocolate in the bowl.
Stir until mostly smooth with just a few flecks of unmelted chocolate. Add the extract, pretzels, and marshmallows to the bowl. Stir to combine. Scoop into a parchment lined loaf pan. Spread with a spatula. Chill until ready to serve.
Slice into 1-inch squares and store in an airtight container in the refrigerator. Enjoy!