Preheat oven to 100 degrees C. Grease a 35x45cm baking tray.
Sprinkle half the chocolate chips on prepared tray. Place in warm oven until chips melt; about 5 minutes. Remove from oven and spread melted chocolate over bottom of tray; set aside.
In a large heavy saucepan over medium-high heat combine butter and brown sugar. Stirring constantly heat until a small amount of syrup dropped into cold water forms hard, brittle threads. Immediately remove from heat. Stir in 3/4 cup slivered almonds and pour onto the tray on top of the melted chocolate; spread mixture evenly.
Sprinkle remaining chocolate chips over the almond layer. The heat from the almond layer will melt the chocolate chips; spread melted chocolate evenly. Sprinkle remaining 1/4 cup almonds over chocolate.
Cut into squares or allow to harden in a solid sheet and break it apart like brittle. Cool completely before removing from tray.