Here is a recipe from King Arthur Flour company that I have loved for years. If you want to impress someone, this is the most fabulous muffin on the planet. I adapted the filling, putting some powdered sugar in because of the cornstarch in it to help thicken it. The xanthan gum helps keep the filling gooey, but was not used in this batch. This picture is taken from my high school cooking class on 'cupcake/muffin' day. One team made these and wow, were they the big hit. All the muffins that day turned out good, but these really are simply sinful!
preheat the oven to 400 degrees. Line a 12 cup muffin pan with cupcake papers, or grease lightly.
perpare topping by mixing the ingredients together until crumbly and set aside. Whisk together all the filling ingredients and set aside.
to make the batter: whisk together the melted butter, milk and eggs. In another bowl, whisk together the dry ingredients, including the chips, stirring until just combined. Add the wet and dry ingredients together until just combined. (this is the muffin method).
Divide half the batter among the muffin cups. Add 2 teaspoons (give or take) of filling on top of that, then finish filling with the rest of the batter. Sprinkle generously with the topping, pressing it in lightly.
Bake 20-25 minutes until golden brown and the muffin top springs back when you gently poke it with a finger. If it sinks in, keep baking a few minutes more.
Remove from the oven, wait 5 minutes and transfer them from the pan to the cooling rack.
To make the glaze, mix the glaze ingredients together until smooth. If its too thick, add a few drops of milk. Drizzle over the cooled muffins.