Step 1

To make the pastry: Toss the butter or the fat in the flour until coated. Add the salt. Add a little ice water and bring the dough together with your hands, sprinkling no more than a few teaspoons of water. On a well-floured surface, shape the dough into a square. Sprinkle more flour onto the square to prevent sticking later; then roll out the dough into a rectangle approximately 1/2 inch thick. Fold the rectangle lengthwise in the shape of an envelope; then roll and repeat. Dust with flour as needed. Repeat this procedure at least 3 or more times, preferably 5 times, taking care not to warm or soften the dough too much as you roll. Cover the pastry with plastic wrap and chill in the refrigerator.

Step 2

To make the filling: Heat a heavy skillet or pan over high heat. Add 1 teaspoon or so of butter. Toss in the kidneys and quickly saute to brown the surface, leaving the interior raw. Remove from the pan.

Step 3

Deglaze the pan with the beef stock, reducing the liquid by half.

Step 4

In the meantime, make the roux: Add the remainder of the butter to a saucepan and melt over low heat. Add the flour, mixing to make a paste. Toast the flour in the butter for a few minutes, until the roux is light golden brown. Add the reduced stock and simmer gently, until the liquid is thickened and coats the back of of a wooden spoon.

Step 5

Bring a pot of water to boil and add the cubed potatoes and turnips. Simmer for 10 minutes, until tender. Drain and set aside.

Step 6

Preheat the oven to 375°F.

Step 7

To assemble the pie: Place the kidney, turnips, and potatoes into a pie pan or ovenproof pot. Cover the ingredients with the gravy so that the liquid comes up to approximately 3/4 of the kidneys and vegetables. Roll out the chilled pastry into a sheet approximately 1/4 inch thick. Carefully lay the pastry sheet over the kidney mixture and crimp the edges with a fork. Puncture the surface once or twice to allow for air vents. Lightly brush the egg glaze over the pastry.

Step 8

Place the pie in the oven and bake for 20 to 30 minutes, until the pastry is golden brown and the interior is very hot. Serve immediately.