Preheat oven to 350 degrees F. Grease and line an 8 x 8 inch pan with parchment paper.
Drain the maraschino cherries and blot them with paper towels to remove any excess liquid. Roughly chop half of the cherries. Cut the remaining cherries in half. Set aside.
In a medium bowl, whisk together the eggs, milk and vanilla.
In a large mixing bowl, combine the flour, baking powder, salt and sugar. Stir well until combined, about a minute.
Add the chopped butter and about half of the egg mixture to the dry ingredients. Mix on a medium speed until the dry mixture starts to moisten. Increase speed to high and continue to mix until it starts to become smooth, about 1 -2 minutes. Add remaining egg mixture and mix well for about a minute.
Stir in the chopped cherries.
Pour into prepared pan and bake for 25 - 30 minutes. Check at about 20 minutes to see if the top is browning too quickly. If so, loosely put foil over the top to finish the baking.
Remove from oven and place on a wire rack to cool for about 10 minutes. Remove from pan and peel off parchment paper. Leave to cool completely on a wire rack.
When cooled completely, dust with powdered sugar, top with extra cherry halves and cut into squares.
Will keep in an airtight container at room temperature for a few days.