Add the butter and Top 'n' Fill to a saucepan over medium-low heat and stir until melted and smooth.
Bring to a boil for 2–3 minutes, then stir through the vanilla and salt.
Remove from the heat and allow the caramel to cool slightly.
Line a 9x9-inch tray with baking paper.
Pour the caramel over the Rice Bubbles and mix until evenly coated.
Press firmly into the tray using a piece of baking paper.
Melt the chocolate and coconut oil together, pour over the top and sprinkle with flaky salt.
Refrigerate for at least 3 hours before slicing into bars.
Keep refrigerated
