1. Prepare an ice bath, and set aside. Melt the butter in a medium saucepan over medium-low heat. Add onions, and season with salt and pepper. Cook, stirring frequently, until onions are translucent, about 8 minutes.

2. Add stock; bring to a boil. Reserve about 1/4 cup each snap and garden peas. Add remaining snap peas to saucepan, and return stock to a boil. Add remaining garden peas; cook until all peas are tender, about 4 minutes. Transfer pan to ice bath. Stir until mixture is cool.

3. Working in batches, transfer mixture to the jar of a blender; process until it is smooth. Return to saucepan, and set over medium heat. Stir in cream, and adjust consistency with more stock, if needed. Season with salt and pepper.

4. Meanwhile, prepare a small ice bath, and bring a small saucepan of water to a boil. Add reserved snap peas and garden peas. Blanch until they are just tender, 2 to 3 minutes. Using a slotted spoon, transfer to ice bath; drain in a colander. Cut snap peas into small pieces.

5. To serve, divide soup among soup bowls, and garnish each serving with blanched mixed peas.