Late one evening second-year student Harry, lacking both practical skills and ethics, decided to sneak into the headmaster's office in search of anything that might help him pass the course. He quickly located the file cabinet, containing one interesting folder in particular labelled "Secret Ingredients", which to Harry's dismay contained just a single sheet of paper:
Secret Ingredient for Cinnamon Swirls:
25688 32076 1274 14976 28188
26730 14036 12672
12432 4368 5916 6732 4394 25536 19604
Harry had no idea what to make of this at all, until he found another crumpled piece of paper in the wastebasket entitled "Secret Ingredient for Cinnamon Swirls (Draft)". On it was a 26 x 26 grid with just a few letters legible: several 'A's along the top row, a 'B' in the bottom right corner of the grid, an 'H' roughly midway down the fourth column and an 'M' roughly midway across the seventh row.
After considering for some time how these two pages might relate to each other, Harry was at last able to identify the professor's secret ingredient for his delicious Cinnamon Swirls. Can you?
(Note: Editorial license lightly taken with the wonderful works of novelist J. K. Rowling, solely for puzzle purposes, is hereby acknowledged.)