- Melt the butter in a skillet over medium heat.
- Add the onions, and cook until tender, stirring occasionally.
- Add the garlic, and cook for about a minute.
- Whisk in the flour with a fork so no lumps form.
- Cook and stir with the fork until browned.
- Remove from heat and set aside.
- Preheat the oven to 350°F (175°C).
- Place the avocado into a blender or food processor, and pour in the milk, cream, lemon juice, salt and pepper.
- Puree until smooth.
- Pour into a heat proof bowl or casserole dish, and stir in the onion and garlic mixture.
- Bake in the oven for 20 minutes, or until thickened.
- Stir in the tequila and cheese, and return to the oven for about 5 minutes to melt the cheese.
- Stir and serve as a fondue.