Place the malted milk balls in a resealable bag and gently hit them several times with a rolling pid or the bottom of the pan. (They should be broken into into chunks with a little bit of crumbs, not completely pulverized.).
Place the butter, sugar and brown sugar in a large bowl and miz with an electric mixer on medium speed for 2 minutes or until completely combined. Add the eggs and vanilla and mix on medium-high speed for 2 minutes until fluffy. Add the malted milk powder and baking soda and mix on low speed for 1 minute or until combined. Add the flour and mix on low speed for 1 minute. Add the smashed malted milk balls and mix for 1 minute until combined. Refrigerate the dough for at least 1 hour.
Preheat the oven to 350°F.
Drop tablespoonfuls of dough onto ungreased baking sheets at least 3 inches apart (they spread a lot).
Bake for 8-10 minutes, or until they just begin to brown on the edges. Remove the cookies from the pan immediately and cool on parchment or waxed paper.