Preheat oven to 400 F degrees.
Cur the pears in half through the stem end. Thinly slice off the cores and any seeds.
Thinly slice the pear vertically, stopping about ½ inch from the stem so the pear slices stay attached at the stem end. Set aside.
Cut black berries into rounds. Set aside.
Lightly flour a clean work surface. Take the dough out of the refrigerator and roll it into a 14-16-inch circle. The dough may seem a little stiff soften as you work it and it warms up. Keep your work surface dusted with flour as you roll the dough to keep it from sticking.
Butter a large baking sheet. Transfer the rolled dough onto the buttered baking sheet (you can either roll or fold the dough to transfer without ripping). Spread the vanilla cream cheese mixture over the center of the circle, leaving about
2-inches of bare dough around the outside edge. Fan the pears in a decorative pattern on top of the vanilla cream cheese, cutting the pear halves in half vertically if necessary, to make them fit. Sprinkle blackberry rounds over pears. Fold the edges of the dough up and over the filling, forming loose pleats all around the edge and leaving the center open.
Whisk remaining egg white and using a pastry brush, brush the edges of the galette with this egg wash.
Melt remaining tablespoon of butter. Brush melted butter over pears and blackberries.
Sprinkle galette crust and fruit topping with tablespoon of brown sugar.
Bake the galette until the pears are tender when pierced with a knife and the crust is golden brown, 50 to 55 minutes. Transfer to a wire rack to cool.