This expression means:
Have I told you how much I love you Dad? I’m your best friend, but this is way more than that, any dog will come meet you at the door, but this is more. I want to do my part to make sure you only have the best things possible. You’ve already got Mom, so good on you! But I can help with other things.
Like that sandwich you’re making. Before you eat it, you should let me do a quick taste test to make sure it’s good enough for you to eat.
This expression is sometimes followed by another one which means, “I couldn’t let you eat a sandwich which already had a bite out of it!”