chocolate - dark, milk or white
Pretty much any nuts will work. Since I have allergies, I'm personally limited to peanuts, but you can use any combination. Pistachios can add a bit of color. The same goes with the fruit...lots of options here; pick your favorites: raisins, dried apricots, dried cranberries, dried cherries, chopped dried mango....candied orange peel or candied ginger also work great.
Chop any of the fruits and nuts that are oversized.
Temper the chocolate.* Cool the chocolate to its working temperature (basic guide would be 84-86° for white, 86-88° for milk, and 88-90° for dark), and work quickly to make your knackerli.
You can pipe the chocolate into discs, oblong bars, crescents, or just about any shape you want. Use a pastry bag (or if you don't have one, put the melted chocolate in a heavy duty zip lock plastic bag and snip off a small corner). Or...pour and spread the chocolate in a thin layer over a baking sheet lined with parchment.
Sprinkle generously with chopped dried fruits and nuts. Let stand at room temperature 30 minutes or until set. If you made a large sheet of bark, break it into rough pieces. Store in an airtight container in a cool, dark location.
* Tempering: Beyond just melting the chocolate, tempering produces a nice glossy finish, a good 'snap' to your cooled chocolates, and prevents the discoloration or "bloom" that can mar your chocolate creations. As a general rule, heat the chocolate until it reaches 110-115°, or 120° for dark chocolate. Then cool the chocolate to it's working temperature (see above) and work fairly quickly to make your creations while the chocolate is still in range.