Place the flour, pecans, sugar, salt and egg yolk in a large bowl. Cut the butter into the dry ingredients using a pastry blender until you have coarse crumbs. When your done cutting the butter into the flour mixture the crumbs should hold together when pressed between your fingers.
Press the crumbs evenly onto the bottom and up the sides of a removable bottom tart pan. When you're patting the crumbs up the sides of the pan, pat them 1/4 inch taller than the edge of the tart pan. Place the crumb lined pan on a large plate and freeze it for 30 minutes to firm the dough and help stop the pastry from shrinking. While your waiting for the tart to come from the freezer preheat your oven to 375 degrees.
After the 30 minutes in the freezer, place the tart pan on a cookie sheet and bake at 375 degrees for 20 - 25 minutes or until very light brown. Remove it from the oven and cool on a wire rack for 10 minutes. Don't turn the oven off, you'll be baking the tart at 375 degrees. But in the meantime, while the crust is cooling....
Peel, core and cut 3 ripe pears in half lengthwise. Cut each halve into six slices. Place the pear slices in a circle (overlapping them) on the bottom of the warm crust. Set them aside a minute while we make the filling.
To make the filling place the following ingredients into a medium bowl:1 large egg1/2 cup heavy whipping cream2 Teaspoons white sugarWhisk the ingredients together until well blended. Add 1/2 cup finely chopped toasted pecans and whisk to incorporate them. Pour the filling over the pears in the tart pan making sure the filling gets into every space in the pan. Bake the tart for 30 minutes or until the filling is set and the pears are tender. Remove it from the oven.Arrange your oven rack about 5 inches from the broiler. Turn the broiler on, sprinkle the top of the tart evenly with one Teaspoon white sugar. Place the tart under the broiler for 1- 2 minutes or until sugar is light brown. Remove the tart from the oven and cool on a wire rack for an hour.