Melt butter in a soup pot over medium-low heat and cook leeks for 8 minutes until soft without browning. Stir in garlic for 30 seconds.
Add broth, 1 cup peas, salt and pepper. Simmer for 8 minutes, then remove from the heat and blend until smooth with an immersion blender.
Stir in cream and return to a gentle simmer. Add tortellini and remaining peas and cook for 3 to 5 minutes, or the pasta package time, stirring carefully until the pasta is tender.
Turn off the heat and stir in Parmesan until melted. Divide among 4 bowls and serve immediately with whole peas and tortellini visible in each portion.