Cook the spaghetti in a large pot of boiling salted water until tender but still firm to the bite, stirring occasionally, about 8 minutes. Drain. Toss with the sun-dried tomatoes. Set aside to cool completely otherwise the hot pasta could curdle the eggs when you add them later on.
In a large bowl, whisk the eggs, salt, and pepper, Parmesan, and fontina to blend. Add the cooled spaghetti mixture; toss to coat.
Preheat the broiler. Melt the butter and oil in a 9 1/2-inch-diameter nonstick skillet over medium heat. Transfer the spaghetti mixture to the skillet, pressing to form an even layer. Cook until the bottom is golden brown, about 3 minutes. Transfer the skillet to the broiler. Broil until the top is golden brown, about 5 minutes. Cool in the skillet to room temperature.
Invert the torta onto a platter. Cut into wedges and serve at room temperature.