Preheat oven to 425 degrees F
Line a muffin pan with liners
In a medium sized bowl mix 2 bags of the Martha White Bluberry Muffin mix with 1 cup of buttermilk, and the zest of a lemon.
Put about 1 Tbs of the mixed up muffins batter in the bottom of each liner.
In a medium size pot, whisk together sugar and corn starch.
Put over medium-high heat and slowly add in buttermilk and lemon, whisking together.
Stir and bring to a boil.
Let boil 2 minutes, then remove from heat and stir.
Add in 2 egg yolks, and whisk it all together.
Return to the heat, and bring to a boil again, stir well, boil 1 minute. It should be nice and thick.
Remove from heat, stir in butter, then stir in sour cream.
Go back to muffin tin, and slightly indent the batter inside the liners to form a well. Put between 1/2-1 Tbs sour cream lemon filling in each muffin.
Spoon additional muffin batter over the top.
You should get 12 muffins, but it will be tight, so try to use batter evenly.
Put in oven and bake 15-17 minutes.
Meanwhile, take remaining sour cream lemon filling and add 1 cup powdered sugar. Whisk until fully incorporated. Set aside
When muffins are done baking, and golden brown on top, remove from oven.
Let cool on cooling rack 5-10 minutes, then put in fridge for 15-20 more.
Dip each muffin in glaze