Preheat your oven to 350°F (175°C).
Line your baking sheets with parchment paper.
In a medium bowl, whisk together the flour, baking powder, and dash of salt. Set aside.
In a large microwave-safe bowl, combine the chopped semisweet chocolate and butter. Microwave in 30-second intervals, stirring in between, until melted and smooth. Allow to cool slightly.
Whisk in the brown sugar until well combined. Then add the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract.
Gradually add the flour mixture to the chocolate mixture, stirring until just combined.
Fold in the coarsely chopped toffee and toasted walnuts.
Scoop heaping spoonfuls of dough onto the prepared baking sheets, leaving space for spreading.
Bake for 10 to 12 minutes, until edges are set but centers are still soft.
Allow to cool on baking sheets for about 5 minutes before transferring to a cooling rack.