If using fresh green beans, bring a large pot of water to a boil. Add all 8 cups of green beans and cook until crisp-tender - 3 to 4 minutes. Drain and run cold water over the green beans. Set aside.: The aroma of boiling water and bright green steam signals the start of texture transformation, and when you plunge the green beans into cold water you lock in their vivid color and firm bite. You want to hear a faint snap when you bite one, not a mushy flop, so timing matters. A common mistake is leaving them in boiling water too long which yields limp, faded beans; use a timer and taste a bean after 3 minutes to confirm crisp-tenderness. When draining, spread them in a single layer briefly to shed excess water, this prevents watering down the sauces later.
Mix soup, milk and pepper in a medium bowl. Stir in 4 cups of the cooked green beans and 2/3 cup Crispy Fried Onions. Spoon this mixture into one side of the divided casserole dish.: As you stir the condensed cream of mushroom soup and milk , you will notice a silky, cohesive sauce forming that clings to each green bean . The aroma is warm and savory, and the addition of the French's Crispy Fried Onions folded in adds an immediate contrast in texture even before baking. The reason this method works is that the condensed soup gives a stable base that will bubble without separating, ensuring an even coating. Watch for clumps when combining; whisk vigorously if needed to smooth the mixture, and avoid over stirring which can mash the beans.
In a small saucepan, heat the cream. Add the Parmesan, lemon juice and spices. Continue to simmer until slightly thickened. Remove from heat. In a large bowl, combine 4 cups of the cooked green beans, the Parmesan sauce and 2/3 cups Crispy Fried Onions. Spoon this mixture into the other side of the divided casserole dish.: As the whipping cream warms you will notice a gentle bubbling along the edges and the kitchen fills with a rich, cheesy scent when the Parmesan melts in. The lemon juice brightens and keeps the sauce from feeling cloying, while the garlic powder , thyme , and sage layer subtle savory notes. Simmer just until the sauce coats the back of a spoon, then take it off heat to avoid over reducing and becoming heavy. Stir the sauce into the green beans so each piece is enveloped. A typical error is overheating and reducing the cream too far, resulting in a gluey texture; keep the heat moderate and lift the pan off the burner when slightly thickened.
Bake the casserole for 30 minutes. Remove from the oven, top each side with 2/3 cup of Crispy Fried Onions. Bake an additional 5 minutes, until onions are golden brown.: When the casserole goes into the oven you will see gentle bubbling along the edges and smell the melding of flavors. After the initial bake the surface should look set with light bubbling; adding the reserved French's Crispy Fried Onions right before the final few minutes ensures they brown without burning. During the extra 5 minutes watch closely through the oven window so the onions reach a deep golden color and crisp texture. Avoid leaving the dish unattended at this stage since the thin fried onions can go from perfect to over browned quickly. The finished casserole will have contrast between creamy interior and crunchy top, and the scent should be toasty with hints of mushroom and cheese.