Hi, my name is Claire, too, but no "i".!
I would find a muffin mix that uses whole wheat flour or has bran or oats added for fiber and toss in the blueberries.
A mix from a box should give the carb count for 1 portion. Look up the carb count for about 1 cup of blueberries (I just got 21.3 gms for 1 cup).
Now, to make a muffin that is approx 30 gms of carbs, add up amount of CHO in 1 portion of muffin mix multiplied by the number of portions in the box. Now add in the gms CHO of your blueberries and the total amount of CHO added from additional ingredients (milk, eggs). you will now have the total amount of gms CHO in entire muffin batch. If you have a high fiber muffin mix, subtract the fibre gms (total for entire box)
Divide the total gms CHO by 30 and that will give you how many muffins you should divide the batch into to make a 30 gm muffin!
This is an example: (made up food label)
muffin mix- 50 gm CHO for 1 cup, 10 servings in a box, 5 gms fiber per serving
50 x 10= 500 gms CHO
5 x 10= 50 gms fiber
500 - 50= 450 gms CHO in muffin mix
now add to this total (also made up numbers)
15 gm CHO for egg
0 gm CHO for oil
15 gm CHO for milk
20 gm CHO for blueberries (this is the real carb count here for 1 cup after 1.8 gm fiber is deducted)
you now have 500 gms total of all ingredients in your bowl.
Divide by 500 by 30= 16.6 muffins
so, if you make 16 muffins with about half left over, you will have 16 muffins with almost exactly 30 gm CHO and one mini muffin for yourself!
Hope this isn't too complicated and let me know if you have questions. i have type one and have to carb count to calculate insulin dosages.