Preheat oven to 180 degrees C or 350 degrees F
Heat a pan on medium heat and add the onion and garlic. Cook for a few minutes until onion starts to soften. Add the spinach and gently stir through to heat for a minute, then remove from heat and set aside.
In a separate pot, set on high heat and melt the butter. As the last of the butter melts, remove from heat and add the flour, stirring through with a spoon to make a paste.
Place pot back on stove on high heat and add 1 cup of the milk, whisking continuously and vigorously to break down the paste and to thicken the milk (this make take a few minutes)
As the milk starts to thicken consistency, add the second cup of milk and stir continuously for 2 minutes.
Add in the grated cheese, garlic and diced basil and stir through for a couple minutes. Sauce will continue to thicken.
Add spinach/onion/garlic mixture to the creamy sauce. Add salt and pepper, stirring through. Once combined, remove from heat
Pour the filling into the bread bowl. Arrange the bread chunks and bread lid on the baking tray around the bread bowl
Bake in the oven at 180 degrees C/350 degrees F for 10 minutes
Remove from oven, gently stir the cheese spinach sauce with a spoon and serve immediately.