In a food processor, pulse together the dry ingredients with the butter.
When the mixture looks sandy or crumbly, add the egg to the mixture. Process again, until the mixture comes together as a dough.
Press the dough into a disc, wrap it in plastic wrap, and freeze it for 20 minutes.
While the dough chills, rinse out the food processor and make the filling.
In a dry pan over low heat, toast 1/2 cup of the pecans until they’re golden and fragrant.
Add all filling ingredients (except the remaining 1/4 cup of pecans) to the food processor and process until they come together to create a thick paste.
Remove the dough from the freezer and lay it on a sheet of parchment paper. Top it with another piece of parchment.
Using a rolling pin, roll the dough into a 12x10 inch rectangle, then put it back into the freezer for 5 minutes (still between the parchment).
Remove the dough from the freezer and slowly peel off the top piece of parchment paper. With the 12-inch side horizontal to you, scoop the filling from the food processor onto the middle 1/3 of the dough.
Using oiled hands, press the filling into a rectangle that goes from top to bottom (10 inches) of the dough, and is about 4-6 inches wide.
Using the parchment underneath the dough, fold one side of the dough over the filling and pat it down. Gently and slowly, peel off the parchment paper and use your fingers to keep the dough on the filling. If the dough tears a little, it can easily be pinched back together.
Repeat with the second side of the dough, folding it on top of the filling and the first side of the dough, then slowly peeling back the parchment paper. Seal the two sides of dough together.
Grab a new piece of parchment paper and lay it on top of the cookie loaf, matching the direction of the cookie (long sides and short sides). Slide one hand under the cookie and parchment paper and hold one hand on top of the cookie and the new piece of parchment paper. Carefully flip it over so that the seam side is down on the bottom, and the cookie sits on the new piece of parchment. Slide your hand out, then slowly peel the old parchment off the top of the cookie and discard it.
Put the new parchment paper and the cookie onto the baking sheet.
Sprinkle the remaining 1/4 cup of chopped pecans onto the top of the cookie, then put it in the oven to bake for 15-17 minutes, until the edges begin to brown.
While the cookie bakes, make the glaze by whisking all of the glaze ingredients together in a small bowl.
When the cookie is done baking, slide the cookie and parchment paper off of the pan, and onto the counter to cool completely.
Drizzle the glaze over the top of the cookie. Once the glaze sets, slice the cookie into 1-inch slices to serve.