Kim Severson’s lovely and poignant Mother’s Day piece in last week’s Food Section sent me sorting through my stash of handwritten, handed-down recipes for one of my favorite fruit-spread vehicles, my mom’s Vanilla Muffins. Fragrant, moist, and simple, these were not muffins you studded with fruit; these were muffins you smeared with fruit. With, say, Aunt Harriet‘s peach butter, made…