Step 1

Place butter in a medium skillet. Melt over medium-high heat, then quickly whisk in flour until smooth.

Step 2

Very slowly, whisk milk and heavy cream into flour mixture until smooth. Bring sauce to a low simmer, stirring occasionally until sauce is slightly thickened.

Step 3

Remove from heat and whisk in Parmesan and pesto until smooth.

Step 4

Meanwhile, prepare pasta according to recipe instructions, reserving 1 cup pasta cooking water.

Step 5

Pour sauce over pasta and gently toss until noodles are coated.

Step 6

Slowly drizzle in reserved pasta water until pasta is creamy.

Step 7

Season pasta with salt and pepper and serve warm with additional cheese if desired.