Preheat the oven to 350°f / 180°c. Line two cookie sheets with parchment paper.
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugars on high speed until pale, light and fluffy. Add the egg and vanilla extract, scraping down the sides of the bowl when necessary.
In a medium bowl, sift together the flour, baking soda, baking powder and salt. With the mixer off, pour the dry ingredients into the mixing bowl. Pulse for a few seconds to gently combine and not cause a flour dust storm, then mix on low just to combine, ten or so seconds.
Add the chocolate and toffee bits and pulse a few times to combine the dough without over mixing.
If you want large round cookies, use a 2 tbs retractable cookie scoop to dole out even balls of cookie dough. I also used a 1 tbs scoop for some of the cookie dough to make them perfect kid’s lunchbox size! Place on parchment paper lined cookie sheets, leaving room for the cookies to spread. You can freeze any leftover dough balls and save to bake later.
Bake the cookies between 11 and 14 minutes, depending on your oven (mine has a fan so I used a slightly shorter baking time) until cookies are lightly golden. Remove from oven, pan-bang as noted above if desired, reform any cookies with an offset spatula back into round shapes if desired, then sprinkle each with a generous pinch of flaky sea salt. Note: you can let the dough rest for an hour, as per Erin’s recipe in the fridge, to help hydrate the dough and develop flavour. Or, you can be a hungry cookie pig and bake them off straight away with similar amounts of deliciousness.