Chocolate-Hazelnut Stuffed Cookies with Sea Salt

Method

1. Prepare the filling: Using a teaspoon cookie scoop or a spoon, form small balls of Nutella, about 1 inch (2.5 cm) in diameter, and place them on a parchment-lined baking sheet. Each ball should contain about 2 level teaspoons of Nutella. You should have about 12 balls.
2. Freeze the Nutella balls uncovered for about 3 hours, or until completely frozen. They can be left in the freezer overnight.
3. Preheat the oven to 350°F. Lightly grease a baking sheet or line it with parchment paper.
4. Make the dough: In a bowl, mix together all the dough ingredients (the 1 cup of Nutella, flour, salt, egg, water, and espresso powder if using) until a cohesive, soft, but not sticky dough forms. The texture should be similar to modeling clay.
5. Using a slightly heaped tablespoon cookie scoop, portion out the dough into 12 equal pieces.
6. Take one piece of dough and flatten it in your palm. Place a frozen Nutella ball in the center. Wrap the dough around the Nutella, enclosing it completely like a dumpling. Roll the ball between your palms to seal any cracks and shape it into a smooth ball. Repeat with the remaining dough and frozen Nutella balls.
7. Place the cookies on the prepared baking sheet. They won't spread much, so all 12 should fit on one sheet. Lightly sprinkle each cookie with a bit of flaky sea salt.
8. Bake the cookies for 8 to 10 minutes. They are done when they have lost most of their shine and you may notice a slight lightening of color around the bottom third of each cookie.
9. Remove from the oven and serve warm or at room temperature. For a molten, lava-like center, serve warm. If at room temperature, the centers will be solid. To reheat, microwave briefly to liquefy the centers again, if desired.