Melt butter in a large saucepan over medium-high heat. Add carrots and onion, season with salt & pepper, and cook, stirring often, until carrots are softened, 15-20 minutes. Stir in broth, coconut milk, and sambal oelek. Bring to a boil, reduce heat, and simmer, stirring occasionally, until vegetables are very soft and liquid is slightly reduced, 40-45 minutes.