In a large pot or deep skillet, melt the butter over medium heat. Add the sun-dried tomato oil, red onion, and garlic. Sauté until the onion is soft and translucent.

Add the sun-dried tomatoes and sauté for a few more minutes. Stir in the lemon zest, tomato paste, and Dijon mustard.

Sprinkle in the flour and stir well. Cook for 1–2 minutes until bubbly and the raw flour smell is gone.

Pour in the Chardonnay, scraping up any bits from the bottom of the pan. Let it simmer until the alcohol cooks off.

Add the lemon juice, chicken stock, and heavy cream. Bring to a full boil, then reduce to a simmer. Simmer for 5–10 minutes, until slightly thickened.

Stir in the Parmesan cheese and chopped parsley. Let it simmer for another 5 minutes.

Meanwhile, bring a large pot of well-salted water to a boil. Cook spaghetti just under al dente, then drain.

Add the drained spaghetti directly into the sauce. Stir well — it will look very saucy, and that’s exactly what you want. With the heat off, stir in 1 cup of mozzarella and let it melt into the pasta.

Transfer everything to a greased 9×13 (or similar) baking dish. Top with remaining mozzarella, grated Parmesan, and fresh parsley.

Bake uncovered at 375°F, middle rack, for 45 minutes, until bubbly and golden.

Remove from the oven and let stand for 10–15 minutes before serving. The sauce thickens beautifully as it rests.