Position rack in middle of oven. Preheat oven to 350°F/180°C.

Spread nuts out in an even single layer on a rimmed sheet pan. Toast nuts for about 12 minutes, shaking pan once during baking time, until evenly and lightly toasted. Cool completely, then chop.

Using the same pan, line it with parchment and lightly coat with nonstick spray; set aside.

Combine butter, sugar, water and 1/4 teaspoon salt in a saucepan and bring to a boil over medium heat, swirling pan now and then top combine the ingredients. Adjust heat so that it is boiling fairly vigorously and continue to cook until a candy thermometer registers 300°F/150°C. The mixture will be a rich golden brown color. It is better to cook a bit longer, than under cook. Quickly stir in the vanilla and baking soda. Allow the bubbling to settle down, swirl pan again and pour toffee out onto prepared pan in to a large puddle. Don’t worry about the freeform shape. Tilt the pan this way and that so until the toffee is even and about 1/4 inch (6 mm) thick or a tad thinner. Immediately sprinkle with chopped pecans and press them gently into toffee to adhere. Drizzle chocolate all over the nuts and sprinkle with salt, if desired.

Let the toffee and chocolate firm up, about 1 hour in the refrigerator. Once the toffee is rock solid, you can break it up into servings pieces. Refrigerate in an airtight container for up to 1 week - if it lasts that long! Ours never has.