To the bowl of a stand mixer, add butter and brown sugar and beat on MED speed until creamed together.
Add in eggs and vanilla extract and mix until combined.
To a small mixing bowl, add flour, baking powder and salt and whisk together to mix.
Add in half the flour mixture and mix on LOW until just incorporated.
Repeat with remaining half of the flour mixture.
Stir in toffee and Butterfinger chips with a wooden spoon.
Cover bowl with plastic wrap and refrigerate for 1 hour or up to overnight.
Preheat oven to 350 degrees and line a baking sheet with parchment paper.
Use a small cookie scoop (or a spoon) to scoop out approximately 1 Tablespoon sized scoops of dough, placing them a couple inches apart on the prepared cookie sheet.
Dip the bottom of a flat-bottomed drinking glass into some granulated sugar and press down slightly to flatten balls of dough just a bit.
Bake for approximately 9 minutes.
At this point, the centers of the cookie will NOT look set, but the edges should be just a little golden brown.
Remove baking sheet from oven and let cookies cool on baking sheet for 2 minutes, then remove cookies to a cooling rack to continue to cool.
Eat cookies as is, or drizzle with some caramel sauce and enjoy!