In a bowl set over a saucepan of simmering water, melt the chocolate with the butter, stirring a few times, until smooth, about 7 minutes.
In a small bowl, sift together the flour and baking powder. Set aside
In another large bowl, using a handheld electric mixer beat the eggs with the sugar at medium speed until thick and pale, about 5 minutes. Beat in the vanilla and salt.
Using a rubber spatula, fold in the melted chocolate a little at a time, then fold in the flour and baking powder.
Stir in the chocolate chips.
Scrape the batter into a shallow baking dish, or bowl, cover and freeze until well-chilled and firm, about 1 hour. You can also keep it in the refrigerator for few hours or overnight. **This step is very important! If you don't chill the dough enough, the cookies will spread all over when you bake them.
Preheat the oven to 350 and line 2 baking sheets with parchment paper. Working in batches, scoop 2-tablespoon-size mounds of dough onto the prepared baking sheets, about 2 inches apart.
If you are adding candy eyes, bake for about 5 minutes, remove from the oven and add the eyes. Return to the oven for another 5 minutes until the cookies are dry around the edges and cracked on top.
If you are not using candy eyes, bake for about 10 minutes until the cookies are dry around the edges and cracked on top.
Let the cookies cool on the baking sheets for 10 minutes, then transfer to a rack to cool completely before serving.