Preheat oven to 400 degrees Fahrenheit.
In a saucepan over medium heat, melt the butter and stir in the garlic. Continue stirring for 30 seconds.
Add in the flour and milk, stirring continuously. Continue cooking for 3 minutes, until the mix has thickened. Then remove the saucepan from the heat.
Add in the crab, white cheddar cheese, lemon juice, jalapeño pepper (keep a teaspoon to the side), and scallions (keep a teaspoon to the side). Optional: Add in the tablespoon of Old Bay for a little extra oomph.
Pour the crab mix into a quart baking dish, then sprinkle the remaining cheddar cheese on top.
Bake the crab dip for 20 minutes, then broil it for 6 more minutes or until the cheese topping turns golden brown.
Remove from oven and let the dip rest for 5 minutes, then sprinkle the remaining scallions and jalapeño on top and serve.