Spinach Salad with Poppyseed Dressing

Make the dressing by blending together the following ingredients in a blender:
1 1/2 Tbsp. poppy seeds
3/4 cup white vinegar
1 1/2 cups salad oil
1 1/2 Tbsp. Grated yellow onion
1 1/2 tsp. salt
3/4 tsp. dry mustard (I have used regular or spicy mustard)
3/4 cup sugar

Blend for 2 minutes in blender and pour over one thinly sliced red onion. Refrigerate over night.
The next day wash and tear into bit size pieces
2 heads of lettuce
2 pkgs. fresh spinach
Toss with:
3/4 lb. grated Swiss cheese (I have used mozzarella)
1/2 lb. bacon, fried crisp
2 cups sliced mushrooms
Pour dressing over salad when ready to serve serves about 16