In a stand mixer fitted with a paddle attachment, mix the flour, salt, and sugar until combined. Add the cubed, cold butter and mix on low until the mixture resembles coarse cornmeal, with just a few pea-size pieces remaining.
Slowly pour in the ice water one tablespoon at a time, being careful not to add in any ice. Pulse until the dough is crumbly but holds together when squeezed.
Turn the mixture out onto a work surface and quickly (so as not to melt the butter) form the dough into a 3/4-inch disk. Wrap tightly in plastic wrap and refrigerate overnight.
In a medium-sized pot, add the strawberries, sugar and cover with water. Bring to a boil and allow to simmer for 45 minutes to an hour.
While the mixture continues to simmer, prepare the slurry by combining the cornstarch and water in a small bowl. Stir until the starch is completely dissolved and the mixture resembles milk. Turn the flame off, add the cornstarch slurry and stir until completely combined.
Bring to a roaring boil and stir continuously for 1 minute. Remove from heat and allow to cool.
Whisk together the egg and heavy cream in a small bowl. Run through a sieve.
Preheat oven to 375°F.
To assemble the hand pies, place the pâte brisée on a floured surface and roll to about 1/4-inch thick. Cut 12 3-inch rounds from the dough.
Using a fork, prick holes in 6 of the rounds. These will be the bottom of the hand pies. One at a time, brush the bottom cutouts with egg wash, top with a slice of Castello Aged Havarti and heap on a tablespoon of the strawberry mixture.
Gently place the top layer of dough over the filling, pressing down with fingers to create a seal. Press a fork into the outside edges.
Place the pies on a baking sheet lined with parchment paper. Brush with egg wash and sprinkle with turbinado sugar. Bake at 375°F for 40 minutes or until golden brown. Allow to cool slightly before serving.
Recipe courtesy of Josh Hager.