Prepare a 9x13 inch sheet pan by lining it completely with parchment paper, ensuring it covers the raised edges.
Arrange the almond brownie brittle squares (or chosen cookies/crackers) in a single layer to fully cover the bottom of the pan. Set this aside for later.
In a sturdy, heavy-bottomed pot, combine the granulated sugar, unsalted butter, salt, sunflower lecithin (if using), and water.
Gently cook the mixture over medium heat, stirring continuously until the sugar has completely dissolved and the butter has melted. Increase the heat to high.
Continue cooking without stirring until the temperature reaches exactly 308°F (153°C) on a candy thermometer. Immediately remove the pot from the heat.
Quickly stir in the whole almonds until they are evenly coated with the toffee mixture.
Carefully pour the hot toffee directly over the prepared brittle squares, spreading it quickly into a smooth, even layer across the pan.
Sprinkle the chopped dark chocolate evenly over the warm toffee. Let it sit undisturbed for about two minutes to allow the chocolate to melt slightly.
Gently spread the melted chocolate into an even layer over the toffee.
Generously sprinkle the chopped almonds over the chocolate layer.
Allow the entire treat to cool completely at room temperature until it becomes firm. Once cooled, break it into delicious, bite-sized pieces.
Store your delightful crispy toffee in an airtight container to keep it fresh and crunchy.