Preheat the oven to 350°F and adjust a rack to the center. Line a baking sheet with parchment paper and set aside.
In medium-sized mixing bowl, combine the flour, almond meal, cocoa powder, baking powder, and xanthan gum. Set aside.
In another medium-sized mixing bowl, gently whisk the eggs to blend them. Mix in the sugar, vanilla and salt.
Make a well in the center of the dry ingredients and pour in the egg mixture. Mix just until everything is evenly incorporated, and then fold in 1 cup of chocolate chips.
Shape the dough into one large rectangle, about 1-inch high and 4-inches wide.
Bake in the preheated oven until it looks dry, about 20 minutes.
Remove it from the oven, let it cool a bit on the baking sheet, and then turn the oven down to 275°F.
Lift the parchment off the baking sheet and use a serrated bread knife to cut the biscotti into slices horizontally, about 1-inch thick.
Line the baking sheet with a new sheet of parchment paper and place each cookie on top.
Return the baking sheet to the now 275°F oven and bake until the biscotti are very dry and becoming golden, about 20 minutes per side. (They can easily be flipped over halfway through the cooking time with a small off-set spatula.)
Let them cool on the baking sheet.
Melt the remaining 1/2 cup of chocolate in a microwave or in a double boiler on the stove-top.
Use a teaspoon to drizzle the melted chocolate over the biscotti. Let the chocolate set at room temperature, about 45 minutes. (To speed this up, you can quickly refrigerate them on the baking sheet.)
These cookies can be stored for up to 4 days in a tightly sealed container in a cool, dark place -- or for up to 3 weeks, in a tightly sealed container in the freezer.