The options for decorating these cookies are endless; we particularly like dipping the cookies in the melted chocolate, but you could also simply drizzle the chocolate on top for sophistication and ease. Or, fill a zipper-lock bag with the melted chocolate, snip off a small corner, and pipe a chocolaty design on top. Use your imagination!
1. Whisk flour, baking powder, and salt together in bowl. Using stand mixer fitted with paddle, beat butter and sugar on medium speed until pale and fluffy, 3 to 6 minutes. Add egg and vanilla and beat until combined, about 30 seconds, scraping down bowl as needed. Reduce speed to low and slowly add flour mixture until combined, about 30 seconds. Mix in toffee bits until just incorporated. Cover bowl with plastic wrap and refrigerate until dough is no longer sticky, 10 to 15 minutes.
2. Transfer dough to counter and shape into rectangular log about 15 inches long and 3 inches wide. Wrap log tightly in plastic and refrigerate until firm, at least 2 hours or up to 3 days.
3. Adjust oven racks to upper-middle and lower-middle positions and heat oven to 350 degrees. Line 2 baking sheets with parchment paper.
4. Slice chilled dough into ¼-inch-thick rectangles and space them 1 inch apart on prepared sheets. Bake until edges are browned, 12 to 16 minutes, switching and rotating sheets halfway through baking. Let cookies cool on sheets for 3 minutes, then transfer to wire rack. Repeat with remaining dough. Let cookies cool completely.
5. Microwave chocolate in bowl at 50 percent power, stirring occasionally, until melted, 2 to 3 minutes. Stir in oil until smooth. Dip part of each cookie into melted chocolate or drizzle chocolate over cookies with spoon. Sprinkle pecans over cookies and let chocolate set, about 1 hour, before serving.