Preheat the oven to 375°F (190°C) and line a 10x14 inch (25 ½ x 35 ½ cm) jelly roll pan with parchment paper.
Cover the pan with a single layer of saltine crackers. Break some in half to fill in edges if you need to.
In a medium saucepan over medium heat, stir together the sugar, butter and salt, and bring to a simmer for about 5 minutes.
Pour the sauce evenly over the crackers, making sure that they are all covered.
Bake until the toffee is bubbling all over, about 6-8 minutes.
Remove from the oven and with an offset spatula, put any crackers that may have moved back in place and let cool for 1 minute.
Sprinkle the chocolate all over the hot toffee and let it rest like this for 5 minutes to melt.
With the offset spatula, spread the melted chocolate evenly over the toffee, then sprinkle all over with the pecans.
Let this cool for a few hours, or until the chocolate has set hard. Break into pieces and serve.
Store in an airtight container at room temperature for up to 2 weeks.
