Line a small loaf pan or square pan with parchment paper and spread out the chopped almonds. and set aside.
In a small saucepan, combine your butter and sugar substitute. On low heat, heat up until the butter has melted and the sugar has dissolved. Stir regularly. Once the mixture begins to bubble, add your candy thermometer into the center of the mixture. Continue to stir every 30 seconds, until the thermometer reaches 300F (hard crack). Remove from the heat.
Once you have removed from the heat, stir continuously to ensure the butter and sugar doesn't separate. Pour into the lined pan and let sit for several minutes.
After several minutes, top with chocolate chips, before covering with tin foil. Let sit for 5 minutes. After 5 minutes, use a rubber spatula to spread out the toffee in an even layer.
Refrigerate until firm. Once firm, break apart into pieces.
To store. Store English toffee in a sealable container. They will keep fresh for at least a week. You can also refrigerate them, and they will keep for at least a month.
To freeze. You can freeze English toffee, but the texture will not be the best once thawed. Wrap toffee in parchment paper and place it in a ziplock bag.