Combine chicken broth, tomato paste, garlic, ginger, lemon juice, garam masala, cinnamon, cumin, sugar, turmeric, and salt in the bowl of your slow cooker. Stir well to mix into a thin paste.
2/3 cup chicken broth or stock, 1 (6 ounce) can tomato paste, 4 garlic cloves, 2 Tablespoons grated ginger, 2 Tablespoons lemon juice, 3 teaspoons garam masala, 2 teaspoons cinnamon, 2 teaspoons cumin, 2 teaspoons granulated sugar, 1 teaspoon turmeric, 1 teaspoon kosher salt
Add chicken and turn to coat, then cut the butter into pieces and dot on top of the chicken.
2-3 pounds boneless, skinless chicken thighs, 4 Tablespoons butter
Cook on high for 3-4 hours or low for 5-7 hours.
When the chicken is cooked through, turn the slow cooker to the keep warm setting, remove the lid, and stir in the cream. Let the cream warm through while you shred or cut the chicken into bite-sized pieces, then return to the pot.
1/2 cup heavy cream
Sample the sauce; if you want it a bit sweeter, add an extra teaspoon of sugar; tangier, an extra teaspoon of lemon juice; more flavorful in general, an extra 1/2 teaspoon of salt.
Serve chicken and sauce over rice with naan, fresh cilantro, and veggies as desired.