Soup: Sauté leeks in olive oil in a large saucepan over medium heat until soft. Add arugula and sauté until wilted. Add the minced garlic and cook for 1 minute. Next add tomatoes, salt, pepper, balsamic vinegar, sugar and white wine. Cook for 5-8 minutes on medium heat to reduce down the wine. Then add fresh basil, cooking until wilted. Pour vegetable mixture into blender or food processor and puree in 2 batches. Pour into a large pitcher. Meanwhile, heat the butter in a large saucepan and add the flour for thickening. Cook the roux for 1-2 minutes on medium heat. Whisk in vegetable broth, vegetable puree and tomato paste. Cook for 5 minutes or longer on medium-high until soup thickens. Whisk in the cream and the milk. Continue to heat at medium temperature; do not boil.
Crostini with garnish: While your soup is heating, prepare cheese spread for crostini by blending cottage cheese, garlic, dried basil, salt and pepper in food processor until smooth. Toast 6 slices of baguette in toaster or oven until golden brown. Spread cheese mixture over toasts and top each toast with 1 arugula leaf, 1 basil leaf and a few chopped cherry tomatoes on each piece. Drizzle balsamic vinegar over each toast. Serve crostini with the soup.
For soup garnish: Laddle hot soup into 6 bowls. Grate fresh parmesan cheese over each bowl. Garnish with a dollop of sour cream, one arugula leaf, cherry tomato half and a drizzling of balsamic vinegar. Serve crostini with soup.