Put the chocolate in a heatproof bowl. Bring a saucepan of water to a simmer. Set a heatproof bowl over the pan, making sure the water doesn't touch the bottom of the bowl. Stir until chocolate is melted and smooth. Set aside to cool slightly.
Whisk the flour, baking powder and salt together in a small bowl.
Beat butter and both sugars in a heavy duty mixer until lightened and fluffy, about 5 minutes on medium speed. Add the eggs, one by one until combined.
Reduce mixer to low and slowly add the melted chocolate. Stir in the flour mixture and chocolate chips. Cover the bowl and chill until the dough is firm and scoopable, at least one hour.
Arrange racks in thirds and heat oven to 350 (175 C) degrees. Line two large baking sheets with parchment paper.
Drop heaping tablespoons of dough onto the pans, spaced 2 inches apart (the cookies will spread). Bake 12-15 minutes, or until edges of cookies are set and center still somewhat soft. Cool on rack 2 minutes, then transfer with a spatula to racks to cool completely.
To glaze the cookies, melt the chocolate in heatproof bowl over a pan of simmering water, stirring until melted and smooth. Dip one half of each cookie into the chocolate, then set on a rack or a parchment-lined pan. Sprinkle the cookies with salt and cool until set.
Glaze the cookies and let them set before serving or packing.
They look and taste best if enjoyed within a day or two.