Dice the chicken thighs into 1-inch pieces and season generously with salt and black pepper.
In a large skillet, heat the olive oil over medium-high heat. Add the chicken and sear for 4-5 minutes until browned on all sides. (The chicken doesn’t need to be fully cooked—just seared to lock in the juices.)
Optional: If your slow cooker has a removable stovetop-safe pot, you can sear the chicken directly in it before returning it to the slow cooker base.
Transfer the seared chicken to the slow cooker. Sprinkle with flour, thyme, rosemary, and ½ teaspoon salt. Stir to coat the chicken evenly.
Add the garlic, onion, carrots, and potatoes. Stir to combine. Pour in the chicken broth and add the bay leaf.
Cover and cook on low for 7-8 hours or high for 3-4 hours until the vegetables are tender.
Stir in the frozen peas and milk, then cook on high for an additional 10-15 minutes until the peas are warmed through.
If the stew is too thick, add a splash of chicken broth. If it’s too thin, whisk in a little extra flour to thicken.
Taste and adjust seasoning with additional salt and black pepper as needed.
Serve warm. Store leftovers in an airtight container in the refrigerator for up to 5 days, or freeze for up to 3 months.