Wash your hands, gather your ingredients, tools, and equipment. 

1. Prepare the garnishes. Cut, crush, or dice any garnishes you're adding and set aside.
2. Chop and melt the large portion of chocolate. Chop the chocolate. Roughly chop any solid bar of chocolate into small, like-sized pieces. Fill a small pot with about an inch of water, and place it over medium heat on the stove. Place about two-thirds of the chopped chocolate in a heat-proof, completely dry bowl, and set it on top of the pot. Be very careful not to let any drops of water near the bowl of chocolate, as even the tiniest bit of water will cause melted chocolate to seize, or harden. Melt over low heat, and stir occasionally until the chocolate is melted and smooth. You can also melt chocolate in the microwave, stirring in between each 30-second burst.
3. Mix in the remaining chocolate. Let the hot chocolate cool slightly. If you have a kitchen thermometer, aim for around 95° F. But about five to ten minutes of cooling should be enough in a room temperature (72° F) kitchen. Add the reserved chopped chocolate and whisk or stir with a spatula until the melted chocolate is completely smooth. If all of the remaining chocolate doesn't melt with stirring, place the bowl back on the pot to warm it slightly and melt the remaining solid pieces. 
4. Garnish and spread. For American-style chocolate bark, mix in your garnishes, using as much or as little as you like. The more you add, the chunkier and chewier the bark will be. On a silicone baking mat or a parchment paper-lined baking pan, pour and spread the chocolate into a loose rectangle. An offset spatula is a great tool for this, but you can use any wooden spoon or flexible spatula you have. No need for perfection, one of the beauties of chocolate bark is its imperfect shape. How thin or thick you spread the chocolate out is up to you. I aim for bark that's about a quarter-inch thick, like a typical chocolate bar. For French-style bark, sprinkle your garnishes now on top of the chocolate after pouring and spreading.
5. Cool and cut. Cool at room temperature until the chocolate bark is hard and set. To make shaped bark, let it cool until almost hard, but still pliable. Press and remove your cookie cutter into the bark and remove carefully. Let the chocolate bark cool completely before pressing the shapes out of the whole. An easy way to get the shaped bark out is by pressing it up from underneath the parchment or wax paper.