Melt butter in a large saucepan or skillet over medium-high heat. Add water and sugars, stirring until melted and bring to a boil. Reduce heat to medium and simmer for 8 to 10-minutes until thickened. Dragging a spoon or spatula across the pan should leave a trail.
Add banana slices, nutmeg, cinnamon, a pinch of kosher salt and cook for 2 to 3-minutes until bananas have softened, but are not falling apart. Keep warm over low heat until ready to serve.
Serve over pancakes, on a Dutch Baby, or over vanilla ice cream.