Step 1

For the creamed spinach: In a medium Dutch oven, melt the butter over medium heat. Add the shallots, garlic and sage and cook, stirring frequently, until the shallots are translucent, about 2 minutes. Add the cream and nutmeg and bring to a simmer over medium heat. Simmer the cream, stirring occasionally, until it is reduced by half, about 20 minutes. Stir in the squeezed spinach, mustard and vinegar. Remove to a bowl and season to taste. Set aside.

Step 2

Preheat the oven to 375 degrees F.

Step 3

For the potatoes: Peel the potatoes and cut into quarters. Place the potatoes in a medium pot and fill with water until the potatoes are just covered. Add a few good pinches of salt to the water. Bring to a boil over medium-high heat and cook until the potatoes are completely tender, 15 to 20 minutes. (Have all the other ingredients out and ready.)

Step 4

Drain the potatoes. For creamier potatoes, pass through a potato ricer into a large bowl. To the warm potatoes, add the milk, crème fraîche, butter, garlic, salt and pepper. Fold gently to combine. If you didn’t use a potato ricer, this can be done in a stand mixer or with a hand mixer. Just take great care not to overmix, as the potatoes can become gummy.

Step 5

Add the creamed spinach to the potatoes and fold to combine. Add the mixture to an 8- or 9-inch square casserole dish.

Step 6

On a lightly floured work surface, roll the puff pastry out until the folds are smoothed. Using your casserole dish as a guide, cut the puff pastry so that it fits flush against the edge of your dish. Set aside the excess.

Step 7

Place the pastry directly on top of the spinach and potato mixture. Using a sharp paring knife, make a diagonal crosshatch design 1 1/2 inches apart in the puff pastry. Do not slice all the way through the pastry.

Step 8

Whisk the egg with 1 teaspoon water in a small bowl. Brush the egg wash over the puff pastry and sprinkle with the Pecorino-Romano. Bake until the pastry is golden brown on top, about 20 minutes. Garnish with additional Pecorino-Romano.