Step 1: Preheat your oven to 350°F (175°C) and grease or line a 9x13-inch baking pan with parchment paper.
Step 2: In a large mixing bowl, combine the flour, oats, brown sugar, baking soda, and salt. Whisk until well combined.
Step 3: In another bowl, cream the softened butter until light and fluffy, about 2-3 minutes.
Step 4: Gradually add the dry ingredients to the creamed butter, mixing until just combined into a thick dough.
Step 5: Transfer the dough to the prepared baking pan and press it evenly into the bottom.
Step 6: Bake the base in the preheated oven for 15-20 minutes until lightly golden brown. Let it cool slightly.
Step 7: In a small saucepan over low heat, combine the Nutella, chocolate chips, and heavy cream, stirring until melted and smooth.
Step 8: Pour the Nutella fudge mixture over the cooled base and spread it evenly.
Step 9: Sift confectioners sugar over the fudge layer for sweetness and presentation.
Step 10: Refrigerate for at least 1 hour, then cut into squares and serve.