Position a rack in the middle of the oven and heat the oven to 350 degrees Fahrenheit.
Put the 6 ounces of butter in a food processor, along with the flour, light brown sugar, cinnamon, and salt.
Pulse until the mixture is well combined (about 20 pulses). (Scatter the dough into a 9-inch-square baking pan and press it evenly over the bottom. Wipe out the processor bowl but don't bother washing it).
Bake the base until firm and lightly browned, about 25 minutes.
When the cookie base comes out of the oven, sprinkle the grated chocolate evenly over the top. (Don't turn off the oven.) Set the pan aside.
As the cookie base bakes, pulse the pecans in the food processor until coarsely chopped.
In a medium-size heavy saucepan, melt the ¼ pound of butter.
Stir in the dark brown sugar, honey, cream, and salt.
Simmer for 1 minute, stirring occasionally. Stir in the pecans.
Pour the pecan mixture over the chocolate-sprinkled cookie base, spreading evenly.
Bake until much of the filling is bubbling (not just the edges), 16 to 18 minutes.
Let cool completely in the pan.
When ready to serve, cut into 16 squares; a bench scraper is the best tool for cutting these chewy bars. Tightly covered, these bars will keep for about five days (though they never last that long).