• 2 c. cubed (1/2-in.) ham
To prepare the crust: Mix the flour and salt together in a large bowl. Using a pastry blender, cut in butter and cheese until pieces are pea-size. (Alternatively, combine ingredients in a food processor and pulse 8 or 9 times. Transfer to a bowl.) Sprinkle the ice water over the top and mix until incorporated. Pinch dough with your fingers; if dough feels dry and does not hold together, sprinkle an additional 1 to 2 tablespoons of ice water over mixture and gently mix until the dough forms large clumps and no dry flour remains. Do not overwork the dough.
Divide dough in half and form each half into 4‑inch disks. Wrap disks tightly in plastic wrap and refrigerate for 1 hour. Let chilled dough sit on counter to soften slightly, about 15 minutes, just before rolling.
To prepare the filling: Melt butter in large saucepan over medium heat. Add leeks and cook, stirring, until the leeks begin to soften, about 3 minutes. Add cabbage and continue to cook, stirring, for another 4 to 5 minutes, until softened. Add flour and cook, stirring constantly, for 2 minutes. Slowly stir in broth and bring to boil over medium-high heat. Stir in potatoes, mustard, thyme, salt and pepper. Bring back to a boil. Reduce heat to low and simmer until sauce is thickened and potato is tender, 5 to 8 minutes. Remove from heat and stir in cream and ham.