Heat olive oil in a large skillet over medium-high heat.
Add beef cubes and brown on all sides, about 5 minutes. Transfer beef to the slow cooker.
In the same skillet, add diced onion and garlic. Sauté for 3 minutes until softened.
Add carrots, celery, and potatoes to the skillet and cook for 3 more minutes, stirring occasionally.
Stir in tomato paste and cook for 1 minute.
Sprinkle flour over the vegetables and stir well to coat evenly. Cook for 1 minute to remove raw flour taste.
Gradually pour in beef broth while stirring to avoid lumps.
Add Worcestershire sauce, dried thyme, dried rosemary, salt, and black pepper. Stir to combine.
Pour the vegetable and broth mixture over the beef in the slow cooker.
Cover and cook on low for 5 to 6 hours, or until beef is tender and vegetables are cooked through.
About 30 minutes before serving, stir frozen peas and corn into the slow cooker mixture.
In a medium bowl, combine 2 cups flour, baking powder, and 1/2 teaspoon salt.
Cut in cold butter using a pastry cutter or fingers until mixture resembles coarse crumbs.
Add 1 cup whole milk and stir just until combined to form biscuit dough.
Turn slow cooker to high.
Drop spoonfuls of biscuit dough evenly over the top of the beef mixture in the slow cooker.
Cover and cook for 25 to 30 minutes, or until biscuits are cooked through and golden on top.
Serve hot and enjoy your slow cooker beef pot pie.