To make the salad, in a large bowl, combine the spinach, orange pieces, and peanuts. Cover and refrigerate until thoroughly chilled.
To make the dressing, in a medium-size bowl, beat the eggs well. Add the mustard, sugar, and salt; beat again. Slowly add 1 cup of the cream and vinegar. Pour into a medium-size saucepan and cook over low heat until thickened. Remove from the heat. Add the remaining 1 cup cream, whisking to combine well.
Serve the well-chilled salad with the hot dressing in a small pitcher on the side.