In a large bowl, whisk together the skyr, minced garlic, grated ginger, and garam masala.
Add the chicken pieces to the bowl and toss until completely coated in the skyr mixture.
Place the chopped red bell pepper and crushed tomatoes into the base of your slow cooker, stirring briefly to combine.
Transfer the coated chicken into the slow cooker, nestling it gently into the tomato and pepper mixture.
Cover and cook on LOW for 4 to 5 hours, or until the chicken is cooked through and very tender.
During the last 10 minutes of cooking, stir the cubed butter into the sauce until completely melted and well incorporated.
Serve the warm stewed chicken curry generously over cooked white rice, garnishing with fresh cilantro and sesame seeds.