In a large mixing bowl sift together the flour, salt & pepper.
Add the butter & work into the flour mixture until a pea sized crumb mixture is formed.
Add the water one tablespoon at a time until the dough begins to come together.
Turn out onto a light floured surface, shape into a disc & wrap in plastic wrap. Refrigerate for 60 minutes while you prepare the filling. Dough can be made 24 hours in advance.
For the filling:
In a large skillet over medium heat add the olive oil, garlic, onions & mushrooms. Cook until the onions begin to turn translucent & the mushrooms begin to soften, about 5 minutes.
Stir in the kale. Season with salt & pepper. Cook for an additional 2 minutes. Remove from heat & let cool to room temperature.
In a separate large mixing bowl whisk together the cream & eggs until fluffy. Season with a big pinch of salt & pepper.
Fold in the kale mixture followed by the feta cheese. Set aside while you roll out the pastry dough.
On a lightly floured surface roll out prepared pastry dough to 1/4 inch thick. Transfer to a 9-inch round pie dish & crimp edges.
Pour the filling into the pie shell & smooth the top to evenly distribute filling.
Bake for 30 minutes at 350(F) degrees, until the top is golden brown & centre has a slight jiggle. Let cool sightly before serving.