Preheat your oven or broiler to 400°F (200°C). Heat a skillet over medium heat and add a tablespoon of olive oil. Add the diced butternut squash and cook, stirring occasionally, until the edges are golden and caramelized, about 8-10 minutes.
1 small butternut squash, peeled and diced, 2 tablespoons olive oil
Stir in the chopped sage and cook for another minute until fragrant. Remove the squash mixture from the skillet and set aside to cool slightly.
1 teaspoon fresh sage, chopped
In a mixing bowl, whisk together the eggs, milk, salt, and black pepper until well combined and slightly frothy. Stir in the grated Parmesan cheese.
6 large eggs, 1/4 cup milk, 1/2 teaspoon salt, 1/4 teaspoon black pepper, 2 tablespoons grated Parmesan cheese
Add the cooled butternut squash mixture and toasted walnuts to the egg batter, gently folding them in with a spatula. This helps evenly distribute the fillings without deflating the eggs.
1 small butternut squash, peeled and diced, 1/2 cup toasted walnuts, chopped
Pour the mixture back into the skillet, spreading it out evenly. Cook over medium heat for about 3-4 minutes until the edges start to set and become slightly golden.
Transfer the skillet to the oven or place it under the broiler, and bake for 12-15 minutes until the top is puffed, golden, and set in the center.
Remove the skillet from the oven and allow the frittata to rest for a few minutes. The residual heat will finish setting the eggs and enhance flavor.
Slice the frittata into wedges and serve warm, ideally garnished with additional sage or walnuts if desired.
