Add flour and salt to a medium sized bowl and whisk to combine. Set aside.
Add butter and brown sugar to a large bowl. Mix until well combined, about 3 minutes of mixing.
Add maple syrup and vanilla and mix, scraping down the sides of the bowl as needed.
Add dry ingredients and mix until partially combined. Add in pecans and toffee, and mix until the dry ingredients are combined.
Lay out two large pieces of plastic wrap. Divide the dough into two, and place each half on a piece of plastic wrap. Form each piece of dough into a log. Wrap in plastic wrap and refrigerate for 1 ½ hours or overnight. You can also place it in the freezer for 45 minutes if you want to bake them sooner.
Preheat oven to 350°F (180°C). Line 2 large baking sheets with parchment paper. Set aside.
Remove cookie dough logs from the refrigerator or freezer. Let set at room temperature for 10 minutes to soften slightly, then cut into ½ inch slices.
Arrange slices on cookie sheets, 1 inch apart from each other. Bake for 10-13 minutes or until you see the sides of the cookie start to brown.
Let cool at room temperature, then store in an airtight container for up to 10 days.