Pound beef cutlets to 0.25-inch thickness using a meat mallet.
Season both sides of the beef with salt and pepper.
In a bowl, combine mozzarella, spinach, garlic, and breadcrumbs.
Place 2 tablespoons of the mixture onto one end of each beef slice.
Roll the beef tightly and secure with a toothpick.
Heat olive oil and butter in a large skillet over medium-high heat.
Sear beef rolls for 3 minutes per side until browned on all sides.
Remove beef from skillet and set aside on a plate.
Add shallots to the skillet and sauté for 1 minute until translucent.
Deglaze the pan with beef broth, scraping the bottom to release fond.
Whisk in heavy cream, parsley, and thyme; simmer for 3 minutes until the sauce thickens.
Return beef rolls to the skillet and simmer for 5 minutes in the sauce until the beef is cooked through and cheese is melted.