COOKIES OF NUTELLA

- Ingredients: 1/2 cup (115g) unsalted butter, softened to room temperature. 3/4 cup (150g) packed light brown sugar. 1/2 cup (100g) granulated sugar. 1 large egg + 1 egg yolk, at room temperature. 1 teaspoon vanilla extract. 1/2 cup (148g) Nutella, divided.