When the butter and sugar are ready, turn off the mixer and use a rubber spatula to scrape down the sides of the bowl. Turn the mixer back on to low speed and beat in the egg and vanilla, making sure to beat until just combined.
Once the egg and vanilla have been incorporated into the sugar mixture, add the flour/baking powder/salt/Ovaltine mixture all at once and continue to beat until just combined.
Line baking sheets with parchment -- this is super important as the cookies have a tendency to stick to the pan. Use a 1-tablespoon cookie scoop to place batter on to the baking sheets, making sure to separate the cookies by 3 inches (the cookies spread while baking).