Preheat oven to 350°F. Melt butter in 3-quart saucepot over medium heat. Add onion and 2 cloves garlic and cook 5 minutes or until tender. Stir in flour and salt and cook 2 minutes, stirring constantly. Gradually stir in milk and bring to a boil. Reduce heat and simmer, stirring frequently, until mixture is thickened and bubbly, about 3 minutes. Add Beemster Mild, Smoked and ½ cup XO and stir until melted.