Set oven to 425 degrees. If using a pizza stone or cast iron pan, place in the oven now while preheating.
Saute’ kale, garlic, and leeks in olive oil with 1/4 teaspoon of salt over medium heat for about 8 minutes. Turn off heat and cover with a lid for 5-10 more minutes until tender. Add sage and parsley. Set aside.
Meanwhile in another bowl combine eggs, anchovy paste, dijon, lemon juice, salt, and pepper.
Roll out dough on a piece of parchment to 1/8 of an inch thick and in an approximate 14″circle. Trim the edges of the dough with a sharp knife to allow them to puff up.
Spread mascarpone cheese on the rolled out circle, all but the outer 2 inches.
Lay filling and grated gruyere cheese on top of the mascarpone.
Whisk together egg wash. Brush the outside 2 inches of dough with the wash.
Fold the outer 2 inches of dough in over the filling, overlapping dough every 2-3 inchesgently pinching just enough to secure.
Pour the seasoned beaten egg mixture evenly over the filling.
Brush top of the crust with egg wash.
Carefully transfer, lifting the parchment and galette onto the stone, cast iron or baking sheet. Sliding onto a pizza peel or cutting board can help with the transfer.
Bake 10 minutes then turn oven down to 375 and bake another 25-35 minutes until puffed and the crust is golden. Cool 20 minutes before cutting.