Here are some possible reasons why your biscotti may not be drying correctly:

 
The biscotti are too moist:
1)  They may not be getting fully baked during their first trip to the oven. 
2)  Your oven calibration may be off and it’s baking at a lower temperature than you’ve actually set.  If this is the case the biscotti aren’t baking enough the first time, and also will take longer to dry even when baked completely.
3) You may not be drying them completely during the second trip to the oven.

Solutions:

1) Rely on visual and textural cues rather than the times listed in your recipe.  After the initial bake the biscotti loaves should be lightly browned, set, and possibly starting to crack on top.  After the drying phase they should be crispy, light, and hard (but not so dry that you’re in danger of cracking a tooth).

2) Get an oven thermometer to test the accuracy of your oven.  If it’s substantially off, have it repaired.

Your chocolate has gotten too hot:
Coating with chocolate can be tricky because of chocolate’s complex chemistry. It’d take a lot of space to go into the specifics of tempering here, and it’s a tricky technique, so your best bet is to try to preserve the crystals already in the chocolate pieces from when the manufacturer tempered it.

Solutions:

1) Use the best quality chocolate you can afford (many of the brands found in grocery stores aren’t really made with coating in mind).   Bittersweet (around 70% dark chocolate) is probably the most common choice, but this is really a matter of personal taste. 

2)  Over a water bath, melt the chocolate at a low temperature while stirring.  Heat only until it’s sufficiently liquid to give you a good coating (keep its temperature below 88-90 degrees (lower if using milk or white chocolate)).  This will hopefully preserve more of the crystals in the pre-tempered chocolate and give you a better looking & faster setting coating.

- Question Submitted by Maurizia

Related Products:
Organic Emmer Flour makes great biscotti and is more nutritious than conventional wheat flour.