English Toffee

Generously butter a large baking sheet. Set aside. Combine butter and sugar in a large heavy saucepan. Cook and stir over high heat until mixture boils. Reduce heat to medium; cook, stirring constantly, until candy thermometer reaches 310°F (155°C). Remove from heat and add 1/2 cup of the almonds. Stir quickly and pour onto prepared baking sheet. When it has cooled somewhat, but is still very warm, sprinkle the semi-sweet chocolate pieces over top. Once softened, spread chocolate with a spatula evenly over toffee. Sprinkle with remaining 1/2 cup of almonds. Cool and and break into serving pieces.