In a small bowl, combine the white rice, wild rice, pecans and dried fruits and season to taste with salt and pepper. Set aside.
In a medium saucepan melt 6 tablespoons of the butter and whisk in the flour. Cook, stirring, for 2 minutes - do not allow the flour to color. Add the milk in a slow but steady stream, whisking constantly, until completely incorporated. Cook until thickened, 4-6 minutes. Whisk in the egg yolks and season with the salt, 1/2 teaspoon of pepper, and 1/2 teaspoon of Essence.
Preheat the oven to 350 degrees F. Grease a 9 x 13" casserole lightly with butter. Spread half of the rice mixture over the bottom of the casserole, top with half of the turkey, then spoon half of the sauce over the top. Top with the remaining rice mixture, then with the remaining turkey, and then spoon the remaining sauce over the top. Sprinkle with the Gruyere and cheddar cheeses and bake, uncovered, until golden brown and bubbly and heated through, 40 to 45 minutes.