In a medium saute pan over medium heat, add butter and brown sugar. Mix and let melt together. Remove pan from flame and stir in the orange liqueur. Remove from the heat and torch the top of the orange sauce using a long kitchen match. Flame will die down after a minute.
In serving bowls, add 2 scoops of ice cream and pour the sauce on top. Garnish with an orange slice.
Use extreme caution when igniting alcohol. Remove the pan from the heat source before adding the alcohol. Pour the alcohol into the pan and carefully ignite with a match or click lighter. Return the pan to the heat and gently swirl to reduce the flames.