The letter reads:
My Dear Boris,
It is lovely, as always, to receive your letters.
Per your question, no, I don't know any potions that can enhance magical power - at least none that are safe to use with any frequency, and I'm not giving you those recipes. I'm sorry to hear that you were rejected by the Wizard's Guild again, but this is not the answer. And there's more to life than throwing lightning at things.
Alchemy is a perfectly respectable branch of magic and you should be proud of your talent with it. When your Uncle William came down with the Sweating Sickness he didn't need the Guild and its fireworks, he needed your alchemy skills. You can and are doing good things with alchemy, even if it's not as glamorous as being on the Guild Council.
Since I can't be there in person to give you a hug, I've enclosed a recipe that should be the next best thing!
With much love,
Mum
A second piece of paper is underneath the letter:
Warm Hug Potion
Ingredients: flowers, sugar, cinnamon