Add the oil to a medium pot and heat over medium heat. Add onions and asparagus stems and saute for 5 minutes. Stir in the milk and parsley and bring to a boil. Reduce heat to low and let simmer for 5 more minutes. Carefully pour into a blender and puree, or puree using a hand blender. Pour back into pot through a fine mesh strainer and return the pot to medium heat. Whisk in the potato soup and the sour cream, and season with salt and pepper. Bring to a simmer, then remove from the heat and serve.
Asparagus and Tomato Tart:
Preheat oven to 375 degrees F.
Place the frozen pie crust onto a baking sheet. Prick the bottom of the crust with a fork and bake for 10 minutes.
Saute the bacon in a skillet over medium heat until crisp. Remove bacon and drain on a paper towel. Add onion and asparagus tips to the skillet with the bacon fat and saute until tender, approximately 5 minutes.
In a large bowl whisk together ricotta, milk and eggs. Add parsley, half the tomatoes and season with salt and pepper. Add asparagus and onion mixture and combine well. Pour egg mixture into the prepared crust.
Bake in the preheated oven for 40 to 45 minutes or until filling has set and the tart is lightly browned on top. Remove from the oven and let cool for 5 minutes. Serve warm or at room temperature.
In a small bowl, toss the remaining tomatoes with the basil, balsamic vinegar and season with a pinch of salt and pepper. Serve as garnish for tart.
When blending hot liquid, first let it cool for five minutes or so, then transfer it to a blender, filling only halfway. Put the lid on, leaving one corner open. Cover the lid with a kitchen towel to catch splatters, and pulse until smooth.