Melt butter in deep skillet over medium high heat (or use slow cooker insert if it's stove-top safe). Sprinkle beef cubes with 2 teaspoons of the salt and 1 teaspoon of the pepper. Sear beef for about 2 minutes per side to form a crust; remove from pan and add into slow cooker.
To the slow cooker toss in the carrots, onion and potatoes. Sprinkle with remaining 1 teaspoon salt and 1 teaspoon pepper as well as the thyme and garlic.
1 tablespoon salt, 2 teaspoons pepper, 3 medium carrots, 1 large onion, 12 small potatoes, 2 tablespoons fresh thyme, 3 cloves garlic
In a small bowl, whisk together beef broth, tomato paste and Worcestershire sauce then pour into the slow cooker along with the Irish stout if using.