8 ounces bittersweet or semisweet chocolate, chopped up
Put the sugar, Lyle's and water or rum in a medium heavy bodied saucepan and bring to a boil over medium heat. Boil 3 or 4 minutes until there are big bubbles. Cover with lid and boil 5 minutes more.
Uncover pan and carefully stir in butter and cook over medium heat until temperature reaches 300 degrees. Remove from heat and add the salt, baking soda and 1 cup sliced almonds. Stir well with a wooden spoon.
Pour onto silpat and spread out with an offset spatula. It's easier to spread evenly if you pour the hot toffee all over the silpat rather than in a pile. Try to get it about 10 x 13 inches. Let cool completely and blot the excess butter on the surface with a paper towel.
Melt chocolate in a heat proof bowl (I like my steel bowl) over a pan of simmering water, stirring occasionally. Spread over toffee with spatula and cover with sliced almonds while chocolate is still warm. Refrigerating the toffee speeds up the hardening of the chocolate; I put the pan in my cold garage for a few minutes. After the chocolate sets up you can cut up the toffee into pieces; they will crack into odd shapes, which just makes things interesting.