Step 1

Bring a large pot of salted water to a boil over high heat. Add the spaghetti and cook, stirring occasionally, for about 8 minutes, or until al dente.

Step 2

Meanwhile, in a medium bowl, whisk the cream, 1/3 cup of the Parmesan cheese, egg yolks, and lemon zest to blend. Season with freshly ground black pepper.

Step 3

Heat a large heavy frying pan over medium heat. Add the oil and bacon and cook for about 5 minutes, or until the bacon is golden brown. Add the squash and zucchini, season with salt and pepper, and cook for about 4 minutes, or until the squash begins to soften. Using a pasta fork, remove the spaghetti from the water and add it to the squash mixture. Reduce the heat to low.

Step 4

Whisk 1/4 cup of the pasta water into the cream mixture to blend. Add the cream mixture to the pasta and squash mixture and toss for about 1 minute, or until the sauce cooks through and coats the pasta thinly (do not boil). Season to taste with salt and pepper. Divide the pasta among 4 plates. Garnish with remaining Parmesan cheese and serve.