In a Dutch oven or similar large skillet, melt the butter and oil over medium-high heat. Add the potato, onion, salt, and black pepper. Sauté until the onion softens, about 5 minutes.

Stir in the garlic, rosemary, and cayenne. Let cook until fragrant, about 30 seconds.

Arrange the chicken in a single layer in a slow cooker. Place the sautéed potatoes and onions on top. Add the corn. Pour in 2 cups of the chicken broth.

Cover and cook until the potatoes are completely tender and the chicken is cooked through, about 2 to 3 hours on low (for breasts) or 4 to 5 hours on low (for thighs).

Remove the chicken from the chowder and set aside on a cutting board to cool slightly. Once cool enough to handle, chop into bite-sized pieces.

With an immersion blender, puree the chowder until it thickens, leaving the texture fairly chunky.

In a medium bowl or large liquid measuring cup, stir together the milk and cornstarch until smooth. Add to the slow cooker. Add in chicken. Stir in the Greek yogurt and bell pepper.

Recover and cook on high for 20 to 30 minutes, until thickened. Adjust the consistency with additional broth if desired.