Preheat your oven to 350°F (175°C) and grease a donut pan.

Whisk together in a large mixing bowl the flour, granulated sugar, baking powder, salt, and ground cinnamon (if using).

Mix the wet ingredients by combining the milk, melted butter, eggs, and vanilla extract.

Combine the mixtures by pouring the wet ingredients into the dry ingredients and stir gently.

Fill the donut pan about halfway with the batter.

Add a teaspoon of chocolate hazelnut spread into the center of each donut mold and cover it with additional batter.

Bake for 10-12 minutes until a toothpick comes out clean.

Cool the donuts in the pan for about 5 minutes, then transfer them to a wire rack.

Prepare the glaze by whisking together the powdered sugar, milk, and vanilla extract.

Dip the cooled donuts into the glaze.

Set the glazed donuts back on the wire rack to let the glaze firm up.

Serve your chocolate hazelnut stuffed donuts warm or at room temperature.