Line a 7x7 pan with parchment paper (a bigger pan can be used but the bigger the pan the thinner your toffee bars will be). Set aside.
In a frying pan lightly roast hazelnuts, stirring frequently so they don't burn. Remove from pan to cool. Roughly chop them and spread them on the prepared pan.
Use a heavy bottom sauce pan, rub butter around the edges of the pan. Combine butter and sweeter. With the heat on low, cook until butter and sweetener are fully melted, this could take up to 10 minutes. Turn the heat up to medium until temperature reaches 300 degrees (hard crack), stirring constantly but gently. STIR CONSTANTLY until the very END - this will prevent your butter from burning and releasing milk solids (you don't want to end up with sweet ghee - although that does sound delicious too). Add molasses for a deeper toffee color but it's totally optional.
Once the mixture has reached 300 degrees remove from heat, set aside for a few minutes. Do not allow for sudden dramatic change in temperature, it could cause the butter to separate.
Stir the mixture with a whisk and pour over the chopped hazelnuts. Allow to cool to room temperature. Refrigerate for one hour until it sets.
In a microwave safe bowl melt 4 mini Aldi bars (4 individual servings) in 30 second increments. It took 90 seconds for my chocolate to melt. You can also use 100% chocolate but you will have to add additional sweetener to make it sweet.
Pour over the toffee and return to the refrigerator for a few hours for the toffee to completely set (I left mine over night).