Cut the stew meat into 1-inch cubes, removing large pieces of exterior fat while keeping any fine marbling. Even pieces cook at the same pace and should look lightly streaked with fat rather than completely lean.

Season the beef with black pepper, garlic salt, and celery salt, then toss it with the flour until coated. The flour should cling in a light, even layer without forming thick dry patches.

Heat 3 tablespoons olive oil in a large skillet over medium-high heat and brown the beef in batches for 45 seconds per side, adding more oil if needed, then transfer it to the slow cooker. Listen for a lively sizzle and look for a dark brown crust before moving each batch.

Lower the skillet to medium heat, melt 1 tablespoon butter, and cook the onions for 5 minutes before adding garlic for 1 minute. The onions should soften and smell sweet, while the garlic becomes fragrant without browning.

Pour in a splash of wine and scrape the browned residue from the skillet with a silicone spatula, then add the onion mixture and remaining wine to the slow cooker. The skillet should be mostly clean, with the dark flavorful bits dissolved into the liquid.

Add the beef broth, bouillon cubes, Worcestershire Sauce, tomato paste, carrots, potatoes, bay leaves, and rosemary. Stir until the tomato paste disperses and the vegetables are surrounded by broth.

Cook on Low for 7 ½ to 8 hours or on High for 3½ to 4 hours. The stew is ready when the carrots are soft, the potatoes are fork-tender, and the beef gives way easily without resistance.

Stir in the frozen peas during the final 15 minutes, then remove the bay leaves and rosemary stem. The peas should be bright green and warmed through, not dull or mushy.

For thicker gravy, whisk the Cold Water and Corn Starch until smooth, then slowly stir it into the stew. Let the stew stand until the broth looks lightly glossy and coats a spoon.

Turn off the slow cooker and swirl in the remaining 2 tablespoons cold butter; add Gravy Master if desired. The butter should melt into a velvety sheen that softens the edges of the broth.