Heat oven to 180°C or 350°F
Lightly spray 2 patty pan tins
Cream butter and sugar until light and fluffy (about 3-4 minutes on high)
Reduce speed and gradually add the egg, then vanilla and mix well
With the mixer on low, add the flour , then the milk alternately, a third at a time. Mix until just combined
Place a heaped tablespoon (or medium cookie scoop) of mixture into pans then bake for 15 mins, until lightly golden and cooked through
Cool in pans for 5-10 mins, then gently twist each cake to release it from the pan. Place the cakes flat side down onto a cake rack to cool completely
If necessary, cut the dome off the top of each cake (otherwise they won't sandwich together nicely). Enjoy the cut-offs, or use them for making cake pops.