In a food processor fitted with a blade attachment add the flour, cheese and butter and pulse until the mixture is crumbly. Add the egg yolk and 3 tablespoons of ice water and pulse until the ingredients just come together.

Turn out onto a lightly floured surface and knead until the dough is smooth. Wrap in plastic wrap and refrigerate for 30 minutes.

Lightly oil six 3½-inch round tart pans. Divide pastry into 6 equal pieces and working one at a time roll out the pastry pieces until they are large enough to line pans. Lift the pastry into pans and press into the side, trimming any excess pastry hanging off the side. Cover and refrigerate for 20 minutes.

Place the pans on a cookie sheet and cover each with a square of parchment paper and fill with dried beans or pie-crust weights. Bake for 10 minutes then remove the paper and beans and bake until golden brown, about an additional 5 minutes. Set aside and allow to cool.

Heat a large sauté pan over medium heat, add the olive oil and heat through. Add the shallots and sauté until soft, about 4 minutes. Add the garlic and cook an additional 30 seconds then add the mushrooms and cook, stirring occasionally, until browned, about 5 minutes. Add the kale, stirring occasionally until the kale is wilted, about an additional 5 minutes. Remove from heat and stir in the cream.

Add the mixture to a large mixing bowl and stir together with the egg and ricotta. Season with salt and pepper.

Divide the filling among tarts and arrange on a baking sheet. Bake until the mixture is set and lightly browned on top, about 25 minutes. Top with walnuts, shaved Parmesan and lemon zest.