Preheat oven to 350° F (180°C).
In the bowl of a stand mixer or using an electric hand mixer, cream together the butter and sugar until light in color and fluffy in texture.
Scrape the sides and add in the eggs and vanilla. Mix until thoroughly combined.
Add in the chocolate cake mix and flour- mix until your soft dough forms.
Add in the crushed peppermint pieces and 1/2 cup (100g) of the white chocolate chips to the dough. Mix until evenly distributed.
Scoop the dough into balls and arrange on a parchment or silicone lined cookie sheet. For small cookies, use 1 1/2 tbsp of dough (#50 scoop), medium cookies use 3 tbsp of dough and for large cookies use 1/3 cup of dough.
Bake at 350° F (180° C). For small cookies: bake 8-10 mintues. For medium cookies: bake 9-11 mintues. For large cookies: bake 13-15 minutes. The cookies will spread and expand slightly and puff up in the center when they are ready to come out of the oven.
Cool the cookies on the pan.
Melt the remaining 1/4 cup (50g) of white chocolate chips in the microwave by placing the chocolate in a microwave safe bowl and heating for 30 seconds at a time until they are melted. Stir at each 30 second mark.
Transfer the melted chocolate into a small zip top bag, snip the corner of the bag and drizzle over the cooling cookies.
Sprinkle with some extra peppermints, if desired.
Enjoy!