If using hazelnuts: Preheat the oven to  350 degree F (177 degree C) and place the hazelnuts on a baking sheet. Bake for about 15 minutes or until fragrant and the skins begin to flake.  Remove from oven and place a dish towel over the nuts.   Let the nuts sit (steam) for a few minutes and then rub the nuts in the towel briskly to remove the skins.  Let cool and then chop coarsely.

If using almonds, walnuts, pecans, and/or macadamia nuts: In a 350 degree F oven bake the nuts for about 8 - 10 minutes or until lightly brown and fragrant. Let cool then chop coarsely. 

Then in a heatproof bowl over a saucepan of simmering water, melt the butter and chocolate.

Meanwhile break or chop the digestive cookies into small pieces (about 1/2 inch). 

Once the butter and chocolate are melted, remove from heat and stir in the digestive cookies, along with their crumbs, and the chopped nuts. 

Spread this mixture into a lightly buttered 8 inch (20 cm) tart or cake pan, cover, and refrigerate for several hours or until set. Cut or break into slices. Store in an airtight container in the refrigerator.

Makes about 10 slices.