Source: The Noshery
(Joy of Baking)
2 cups (170 grams) sliced or slivered almonds, toasted
1 1/4 cups (270 grams) firmly packed light brown sugar
2 tablespoons water
1/2 cup (113 grams) unsalted butter
1 tablespoon light corn syrup
1 teaspoon (4 grams) pure vanilla extract
1/4 teaspoon baking soda
6 ounces (170 grams) bittersweet or semisweet chocolate, coarsely chopped
Preheat oven to 350 degrees F (177 degrees C). Place almonds on a baking sheet and bake them for 8-10 minutes, or until golden brown and fragrant. Set aside to cool.
Once the almonds have cooled, place in a food processor, fitted with a metal blade, and pulse the almonds until they are finely chopped. Sprinkle half of the nuts in an 8 inch by 10 inch buttered or oiled baking sheet. Set aside.
In a medium-sized, heavy saucepan combine the brown sugar, water, butter, and corn syrup. Have the baking soda and vanilla extract ready. Bring the sugar mixture to a boil and cook, stirring as little as possible with a wooden spoon, until the mixture reaches 285 degrees F (140 degrees C). Immediately remove the saucepan from the heat as the temperature will continue to rise to 290 degrees F (145 degrees C). Add the baking soda and vanilla extract and stir to combine.
Immediately pour this mixture evenly over the nuts on your baking sheet. Then place the chopped chocolate over the hot toffee. After a few minutes the chocolate will be soft enough to spread with an offset spatula in an even layer over the toffee. Sprinkle the remaining chopped almonds over the melted chocolate.
Cool completely, refrigerate for 30 minutes and then cut into desired shapes using a sharp knife or break into pieces using hands.
You can store the toffee, in an airtight container at room temperature, for about 7-10 days.