Preheat the oven to 350 degrees F with racks in the upper and lower thirds. Line 2 large baking sheets with parchment paper.
Whisk the flour, baking soda and salt together in a bowl.
Combine the butter and sugars in a large bowl and beat with an electric mixer at medium-high speed until light and fluffy. Beat in the eggs one at a time. Beat in the vanilla and 2 teaspoons water.
Add the flour mixture and beat until just incorporated, then beat in the chocolate chips, toffee and walnuts, if using.
Spoon slightly rounded tablespoons of dough onto the baking sheets about 2 inches apart. Bake the cookies, switching the position of the baking sheets halfway through, until the edges of the cookies are deep golden brown and the tops are golden, 10 to 12 minutes. Cool a few minutes on the baking sheets, then transfer to a rack to cool completely. Bake the remaining cookies in the same manner, letting the baking sheets cool completely between batches.