For the Breadcrumbs: Add 1 ½ tablespoons of butter to a large pot over low heat. Once melted, mix breadcrumbs and thyme into the butter. Cook for 2-3 minutes, until the breadcrumbs are slightly toasted and browned; do not burn. Remove the breadcrumb mixture from the pot; set aside.
Prep the Cheese: Remove the rind from the brie cheese and cut it into cubes. Shred the cheddar and parmesan cheese.
For the Cranberries: Grate the frozen cranberries using a grater and set them aside. This can be done by hand or with a food processor.
For the Pasta: In the same pot, add 3 tablespoons of butter over medium low heat. Once the butter has melted, add in the garlic and shallots; mix well and cook until fragrant (1-2 minutes). Add the dry pasta into the pot with the melted butter, garlic, and shallot; mix well.
Add 2 cups of vegetable broth into the pot; mix well. The shells may not be fully covered. Continue to stir, every 2-3 minutes, while the broth cooks down. Cook for 5-7 minutes.
Once the vegetable broth is cooked down, add another 1 cup of vegetable broth. Stir the mixture repeatedly for an additional 5 minutes.
Continue stirring for another 5 min until broth cooks down leaving some broth at the bottom of the pot.
Remove the cooked pasta from the heat and add in the heavy cream, brie, cheddar, and parmesan cheese; add pepper to taste and mix well.
To Serve: Pour pasta into a serving dish or bowls. Top with breadcrumbs, grated cranberries, and thyme leaves.
