Step 1

In a large bowl, whisk together the flour, salt, and sugar.

Step 2

Sprinkle the butter all over the flour. Use your clean hands to squish the flour and butter together until you get a crumbly mixture. Add ½ cup of sour cream and mix with a fork until the flour is moist (if you find it too dry, add more sour cream, but a maximum of another Tablespoon).

Step 3

Transfer the dough to a lightly floured work surface and using your hands shape it into a ball. Use a knife to cut the ball in half. Form into two disks. Flatten each half into a disc (form the disks so that there are no cracks) and wrap in cling wrap. Place in the refrigerator for at least 1 hour.

Step 4

In a large bowl, gently toss blackberries with honey, lemon juice, thyme, vanilla, and cornstarch; set aside.

Step 5

Remove one pie dough disc from the fridge, and on a lightly floured surface roll it out into a roughly circular shape about 12 inches in diameter. Transfer the rolled-out pie dough into the 9-inch pie dish, and shape it so that it's snug against the dish sides.

Step 6

Separate the egg white and egg yolk. Beat the egg white in a small bowl and brush the dough and its edges with half of the beaten egg white. Chill in the refrigerator while you roll out the top crust.

Step 7

Roll out the second ball of pie dough for the top crust. Spoon the berry mixture into the dough-lined pie dish.

Step 8

Top the pie with the remaining crust by weaving a lattice design or cut slits to vent a solid crust. Fold the edges back over themselves and use your fingers to crimp to seal the edges.

Step 9

Place the pie back in the refrigerator for 45 minutes or in the freezer for 15-20 minutes.

Step 10

When ready to bake, preheat the oven to 400 °F place the rack on the lower third with a baking sheet inside.

Step 11

For the egg wash, add the yolk to the rest of the egg white, and whisk.

Step 12

Just before baking, brush the top of the pie with the beaten egg and sprinkle with sugar.

Step 13

Bake for 15 minutes, then reduce temperature to 350 °F and bake for additional 35-40 minutes or until the filling is bubbling and the crust is golden brown.

Step 14

Remove from oven and let cool before slicing.

Step 15

Top with ice cream or whipped cream, if desired. Store leftovers in the refrigerator for up to 3 days.