Line a 13x9-inch baking pan with parchment paper and set aside.
Combine butter, sugar and salt in a saucepan; cook over medium-heat, whisking constantly for 8 minutes.
Stir in almonds and pretzels; continue to whisk and cook for 2 more minutes.
Remove from heat and whisk in vanilla and espresso powder.
Immediately pour the toffee into the previously prepared pan.
Let stand 2 minutes, then sprinkle with chopped chocolate; spread evenly to cover the entire surface.
Sprinkle with crushed pretzels, gently pressing into the chocolate.
Let stand 2 hours, or until completely cooled.
When the toffee has hardened, break it up in pieces.