Bring the chicken broth, 1 cup water and the bay leaves to a simmer in a medium saucepan over medium heat.
Meanwhile, melt 3 tablespoons butter in a medium dutch oven over medium heat. Add the leeks and cook, stirring occasionally, until softened but not browned, about 4 minutes. Stir in the orzo and thyme; season with salt and pepper. Add the warm broth mixture and adjust the heat to maintain a simmer. Add the heavy cream and simmer, stirring occasionally, until the orzo is al dente and most of the liquid is absorbed, 8 to 10 minutes.
Remove the bay leaves. Stir the remaining 1 tablespoon butter, the parsley and the lemon zest and juice into the orzo; season with salt and pepper.