In a heavy-bottomed soup pot or Dutch oven, cook the bacon until well done and slightly crisp.
Transfer the bacon to a bowl, straining away the grease.
Drain all of the bacon grease out of the pot but do not wipe the pot clean; leave any stuck bacon bits in the pot too.
Add the olive oil, butter, onion, carrots and celery to the pot.
Over medium heat, stir and cook the vegetables for 5 to 7 minutes.
Add the salt, ground black pepper, minced garlic and fresh thyme leaves; stir well and cook for 3 minutes.
Next, stir in the flour until well absorbed.
Once no trace of the flour remains, continue to cook the flour with the onions and garlic mixture for 3 minutes.
Pour in the vegetable broth, half a cup at a time, whisking it well into the flour mixture after each addition.
Pour in the milk, half a cup at at time, continuing to whisk well after each addition.
Continue to cook for 3 to 5 minutes until the sauce mixture thickens.
Add the frozen pierogies and the frozen chopped kale to the pot; stir well to incorporate and cook until the soup returns to a simmer.
Stir often to prevent the pierogies from settling and sticking to the bottom of the pot.
Once the soup comes back to a low simmer, continue to cook for 5 minutes, stirring often.
Finally, add the shredded cheese; stir to combine and cook just until the cheese is melted.
Plate the soup and top with the bacon crumbles.
Garnish with dill sprigs, bits of grated cheese and/or sour cream (optional).
