Preheat the oven to 350 degrees F (175 degrees C).
Press the pie pastry into the bottom and up the sides of a 9 inch pie plate. Flute the edges.
Place the pear halves cut side down in the pie crust with the small ends toward the center.
In a medium bowl, mix the butter and sugar together until smooth, then beat in the eggs one at a time until light and fluffy. Stir in flour and vanilla.
Pour over the top of the pears.
Bake for 1 hour in the preheated oven, until pears are soft and custard is set in the center. Cool completely before slicing and serving.