You can make your chocolate frame any size you would like, however, if you were planning to use it around a chocolate "canvas", your frame should be the appropriate size. Whatever the case, your first step is to make the frame template. If you want your frame to be square, you will only need one piece of wood, if you would like it to be rectangular, you will need two. Choose a piece of wood that is the length and texture you would like for your frame. Using a mitre box, cut the one or two frame template pieces exactly to size. Both ends should be cut on an angle, and the back should have 2 nails sticking out of it.
Using a whisk, lighten the flour by incorporating a little air. Spread a 2-inch thick layer of flour on top of a large sheet pan (or directly on the work surface, if the frame you are making requires more space). The amount of flour required will depend on the size of the chocolate frame. Press each piece of the frame template into the flour, immersing it completely and using even pressure, then carefully and delicately lift it out. Place the bittersweet chocolate in a piping bag with no tip. Placing the tip of the piping bag as close as possible to the flour/relief, carefully fill the space with chocolate and allow it to set for about 30 minutes. When the chocolate has set, lift it from the flour. If you would like an antique look, leave the flour on the chocolate piece, otherwise, clean it off using a strong bristled pastry brush or nailbrush.
Please note: It is better to place the melted chocolate in a piping bag and pipe it into the flour. If you pour the chocolate from a spouted container, the weight of the chocolate as it falls can damage the delicate flour mold.
If you are using a chocolate canvas, place it on the work surface in front of you. Position the chocolate frame pieces on top of the canvas along the edges. Trim to fit if necessary. Lift one frame piece and, using a cornet filled with chocolate, draw a line directly onto the canvas in its place. Reposition the chocolate frame piece so it is "glued" to the canvas. Repeat with the other three frame pieces.
To finish, you can use a pastry brush dipped in vegetable oil to apply a thin coat to the chocolate frame. This will give it a slight shine.
Special Equipment: Wooden frame template.
How to Temper Chocolate(From Dessert Circus, Extraordinary Desserts You Can Make At Home by Jacques Torres):
Chocolate is tempered so that after it has been melted, it retains its gloss and hardens again without becoming chalky and white (that happens when the molecules of fat separate and form on top of the chocolate). There are a variety of ways to temper.
One of the easiest ways to temper chocolate is to chop it into small pieces and then place it in the microwave for 30 seconds at a time on high power until most of the chocolate is melted. Be very careful not to overheat it. (The temperature of dark chocolate should be between 88 and 90 degrees F, slightly warmer than your bottom lip. It will retain its shape even when mostly melted. White and milk chocolates melt at a temperature approximately 2 degrees F less because of the amount of lactose they contain.) Any remaining lumps will melt in the chocolate's residual heat. Use an immersion blender or whisk to break up the lumps. Usually, chocolate begins to set, or crystallize, along the side of the bowl. As it sets, mix those crystals into the melted chocolate to temper it. A glass bowl retains heat well and keeps the chocolate tempered longer.
Another way to temper chocolate is called seeding. In this method, add small pieces of unmelted chocolate to melted chocolate. The amount of unmelted chocolate to be added depends on the temperature of the melted chocolate, but is usually 1/4 of the total amount. It is easiest to use an immersion blender for this, or a whisk.
The classic way to temper chocolate is called tabliering. Two thirds of the melted chocolate is poured onto a marble or another cold work surface. The chocolate is spread out and worked with a spatula until its temperature is approximately 81 degrees F. At this stage, it is thick and begins to set. This tempered chocolate is then added to the remaining non-tempered chocolate and mixed thoroughly until the mass has a completely uniform temperature. If the temperature is still too high, part of the chocolate is worked further on the cold surface until the correct temperature is reached. This is a lot of work, requires a lot of room, and makes a big mess.
A simple method of checking tempering, is to apply a small quantity of chocolate to a piece of paper or to the point of a knife. If the chocolate has been correctly tempered, it will harden evenly and show a good gloss within a few minutes.