Preheat oven to 350 degrees F. Line 9 x 13-inch baking pan with parchment paper and generously grease. Set aside.
In a large bowl, sift together cocoa powder and malted milk powder. Add flour, baking soda, baking powder, salt, and sugar. Whisk together.
In a small bowl, combine melted butter, milk, oil and vanilla. Add to dry ingredients. Use a sturdy whisk to mix together. Continue to beat until mixture is smooth. Transfer batter to prepared baking pan, spreading into an even layer.
Bake for 30-35 minutes until toothpick inserted in center of cake comes out clean. Allow cake to cool in pan for 10 minutes before unmolding. Allow cake to cool to room temperature on wire rack.