Spiced rum provides depth and complexity to this bracing and delicious punch. It may well be the hit of your next get-together. Use a soy-free vegan butter for soy-free punch.
Combine the sugar, butter, agave, cinnamon, nutmeg, cloves, and vanilla in the slow cooker and stir until well blended. Add the rum and the boiling water. Stir to blend well. Cover and cook on Low until hot, 45 minutes to 1 hour.
Serve hot in mugs and garnish with cinnamon sticks. If not serving right away, turn the slow cooker to the Keep Warm setting.