In a saucepan melt butter over low heat. Add sugar and lecithin and stir constantly with a wooden spoon over medium heat. When mixture comes to a boil, add the corn syrup and continue stirring constantly to prevent burning until temperature reaches 300 degrees F on a candy thermometer.
After mixture reaches 300 degrees F, remove from heat and add salt and chopped almonds, if using, and mixing gently. Pour into a well buttered shallow pan. Depth of toffee should be approximately 1/4-inch.
Before toffee sets, score with a knife into uniform pieces. Toffee should be stored in an airtight container.