Step 1 — Build the sauce base Add the butter pieces, dark brown sugar, rum, vanilla extract, cinnamon, nutmeg, and salt to the slow cooker insert. Give it a brief stir — the mixture will look rough and unincorporated at this stage, which is completely normal. The heat will do the work.

Step 2 — First cook Cover and cook on LOW for 1 hour, lifting the lid to stir once at the 30-minute mark. By the end of the hour the butter and sugar will have fully melted and combined into a glossy, dark, fragrant caramel sauce. Taste it. Try not to eat it all immediately.

Step 3 — Thicken the sauce In a small bowl, mix the cornstarch and cold water together until completely smooth with no lumps. Pour the slurry into the slow cooker and stir thoroughly to distribute it evenly through the sauce. This step thickens the sauce just enough to cling to the bananas rather than pooling thinly at the bottom of the bowl.

Step 4 — Add the bananas Nestle the banana halves into the sauce cut-side down, arranging them in as close to a single layer as possible. Spoon a little sauce over the exposed tops so they cook evenly on all sides. Cover and cook on LOW for a further 45–60 minutes. Check at 45 minutes — the bananas should be tender when pressed gently but still holding their shape, and the sauce should be thick and syrupy, coating the back of a spoon. Give it an extra 10–15 minutes if needed.

Step 5 — Serve immediately Place generous scoops of vanilla ice cream into bowls or onto plates, lay 2 banana halves alongside or over the top, then spoon the warm caramel sauce over everything with real generosity — don’t be shy with it. Finish with chopped pecans if using. Get it to the table fast. The temperature contrast is everything.