1. Preheat the oven to 350 F. Grease and flour two baking sheets or line the baking sheets with parchment paper.
2. In a small bowl, sift together the flour, salt and baking powder; set aside.
3. Melt the butter and bittersweet and semisweet chocolate in the top of a double boiler over boiling water. Whisk the butter and chocolate until blended and cool.
4. In a medium bowl, beat the eggs and sugar with a handheld electric mixer on medium-high until lemon colored, about 1 minute. Add the chocolate mixture and the vanilla and beat until combined. Stir the flour mixture into the batter gradually, so there will be no lumps. Stir in the toffee bits.
5. Use a small ice-cream scoop to scoop out 1 1/2-inch mounds of dough and place them about 3 inches apart. Dip the ice-cream scoop in hot water before scooping each cookie to prevent sticking.
6. Bake the cookies for about 10 to 12 minutes, or until the tops barely spring back and are slightly puffed. Transfer to a rack and cool. Store in an airtight container until serving.
Recipe notes: The cookie dough can be made through Step 5, covered, and refrigerated for up to one day before continuing with Step 6. The cookies can be made up to three days ahead of time and stored in an airtight container.