Preheat the oven to 400°F and grease a 12-cup muffin pan. Cut the cream cheese into 12 small cubes and keep them in the fridge until needed.
In a large bowl, whisk together the flour, baking powder, baking soda, salt, garlic powder and sugar. Stir in 1 1/4 cups of the cheddar and the green onions so they are coated in flour.
In a separate bowl, whisk the buttermilk, sour cream and melted butter until smooth.
Pour the wet ingredients into the dry ingredients and fold until just combined. The batter will be thick and a little lumpy, which keeps the muffins soft and fluffy.
Spoon a heaping tablespoon of batter into each muffin cup and press a cream cheese cube into the center. Cover with the remaining batter so the cream cheese is hidden, then top with the remaining cheddar and the everything bagel seasoning.
Bake for 18-22 minutes, until golden brown and a toothpick inserted into the muffin, not the cream cheese center, comes out clean.
Let the muffins cool in the pan for 5 minutes and serve warm. Leftovers can be rewarmed in the microwave for 15 seconds to soften the creamy center again.