Preheat oven to 425.
Roll out half of pastry on a lightly floured surface and line bottom of a 9 inch pie plate. Do not prick. Set pastry shell aside.
In a medium-size bowl, whisk egg yolks with butter.
Stir sugar with flour.
Then, stir into egg yolk mixture to form a paste.
Stir in blackberries and pears until well mixed.
Turn mixture into pie shell.
Roll out remaining dough and cut into strips 1/2 inch wide. Weave strips over filling to form a lattice top.
Bake at 425 on the bottom rack for 10 minutes, just until edges start to brown.
Then, reduce oven temperature to 350 and continue baking for another 40 minutes.
Let cool for at least an hour...I know it's tempting to grab a spoon and dig right in, but try to have some self restraint.