• Begin by preparing the dough.

For the dough:

• Using a handheld cheese grater, grate butter into a small bowl, then freeze for 10 minutes.
• While butter freezes, combine flour, salt, and sugar in large mixing bowl.
• Place cold grated butter and flour mixture in a food processor and pulse until you get mealy texture.
• Slowly begin adding water, 1 tablespoon at a time, pulsing until dough takes shape.
• Dump the dough onto lightly floured surface before shaping into a flattened round. Wrap in plastic wrap, and refrigerate for 45 minutes until dough is firm and cold.
• While the dough chills, prepare the filling.

For the filling:

• In a large skillet over low heat, heat the oil.
• Add onions and stir to coat.
• Cook over medium low heat, stirring occasionally, until onions are soft and golden brown. This takes time (30 to 35 minutes).
• Remove from the heat and allow to cool.
• Season with salt and pepper.
• Preheat oven to 375° F.
• Line baking sheet with parchment paper.

To assemble:

• Roll out the chilled dough into a ⅛″ thick sheet, then transfer to the parchment-lined baking sheet (you can use store bought if you prefer).
• Spread a thin layer of dijon mustard on the dough leaving a border of 2 inches.
• Spread the chopped kale and half the herbs and half the cheese over the mustard. Pile the caramelized onions over the kale and spread evenly, leaving a 2 inch border.
• Sprinkle the rest of the herbs and the rest of the cheeses over onion filling.
• Fold edges of dough over filling, pleating as you fold.
• Brush dough with egg and sprinkle with sesame seeds.
• Bake on the middle rack for 30-35 minutes until the crust is golden.
• Remove from the oven and allow to cool slightly before cutting.