Preheat oven to 350°F. In a large bowl of a stand mixer, using the wire whip attachment, beat eggs on high speed for 5 minutes or until thick, at least double the size, and the egg mixture turns a light yellow colour.
Gradually add sugar, beating until the mixture is light and fluffy (about 2-3 more minutes). Beat in vanilla.
Combine flour and baking powder in a small bowl. Gradually add to batter, beating at low speed until smooth.
Heat milk and butter in a small saucepan until melted. Gradually add to batter; beat on low speed until just combined.
Pour into a greased 10-in. spring foam pan. Bake at 350° for 35-40 minutes or until a toothpick inserted near the centre comes out clean.