Step 1

Heat oil and butter in a large heavy pot over medium heat. Add bacon and cook, stirring often, until fat is rendered and bacon is crisp, 5-8 minutes. Add leeks and season with salt. Increase heat to medium-high and cook, stirring often, until leeks begin to brown, 5-8 minutes. Add cream, thyme, and 1/2 cup water. Bring to a boil, reduce heat, and simmer, stirring occasionally, until sauce is thickened and coats the back of a spoon, 5-8 minutes.

Step 2

Meanwhile, cook pasta in a large pot of boiling salted water, stirring occasionally, until al dente. Drain pasta, reserving 2 cups pasta cooking liquid.

Step 3

Add pasta, Parmesan, and 1 cup pasta cooking liquid to sauce and stir to coat. Increase heat to medium and continue stirring, adding more cooking liquid as needed, until sauce coats pasta.