Step 1: In a large saucepan, heat butter oven over medium-high heat; saute mushrooms and onion until tender.

Step 2: Mix flour, salt, pepper, and 1 can broth until smooth; stir into mushroom mixture. Stir in the remaining can of broth. Bring to a boil; cook and stir until thickened, about 2 minutes. 

Step 3: Reduce heat; stir in cream. Simmer, uncovered, until flavors are blended, about 15 minutes, stirring occasionally.