STIR raisins with hot water in a small bowl. Let stand until plump, about 10 min. Drain well.
PREHEAT oven to 350F. Line 2 baking sheets with parchment.
STIR oats with flour, baking soda and salt in a medium bowl. Beat butter with sugar in a large bowl, using an electric mixer, until fluffy, 3 min. Beat in egg and vanilla. Stir in oat mixture, using a wooden spoon. Stir in raisins. Spoon 2-tbsp portions of dough 3 in. apart onto prepared sheets. Flatten them slightly, using your fingers.
BAKE in centre of oven until edges are golden but centres are soft, 10 to 12 min. Transfer cookies to a rack to cool completely. Cookies keep well at room temperature up to 1 week.
How to cream butter and sugar
Nutrition (per cookie)
A lesson on butter
Soft butter: when butter and sugar are creamed together, air is incorporated evenly in the base of a batter or dough. It creates tenderness and lift in baked goods. Use it in: cakes and soft cookies.