Using a hand or standing mixer, cream butter, sugar and brown sugar until nice and creamy. Add in vanilla and egg and beat until incorporated. You don't want to over do this part or cookies will be stiff. Just enough until the egg is mixed in (about 20 seconds.): You will notice a change in texture as the butter and sugar transform into a paler, airy mass that smells sweet and slightly caramelized; that airy feel creates lift and tenderness in the baked cookie. As you add the vanilla and egg , stop when the mixture becomes homogeneous and glossy, because overbeating incorporates too much air and can make the dough tough and the cookies cakier. A common mistake is to beat for too long after adding the egg , which warms the dough and causes spreading in the oven. If the mixture feels greasy or separates, chill it briefly to bring it back together, and always scrape the bowl so everything mixes evenly.
In a separate bowl, whisk together flour, sea salt and baking soda. Mix dry ingredients into wet ingredients until combined.: The dry ingredients should look uniform and pale, with the baking soda fully distributed so that each bite rises evenly. When you fold these into the creamed mixture, the texture will change from glossy to a thicker, slightly tacky dough that holds shape. If you still see streaks of flour, mix gently until they disappear, because under-mixed dough yields pockets of dry flour. Avoid overmixing, which develops gluten and makes cookies chewy rather than tender; use a rubber spatula and stop as soon as the dough is uniform.
Stir in chocolate chips and candy canes.: At this stage, the dough becomes visually exciting, studded with shiny white chocolate chips , darker chocolate chips , and flecks of crushed candy canes . The peppermint aroma will start to lift from the bowl. Fold slowly to distribute the mix-ins evenly without smashing them into fragments, because too much crushing releases oils and sugars that can alter texture. If you notice large candy cane chunks, crush them finer or remove the biggest bits to prevent melting and streaking during bake time.
Chill the dough for about 30-60 minutes, seal tightly and chill up to 3 days before baking. Allow to sit out 10-15 minutes before you bake them if you chill longer than about 2 hours.: Chilling firms the dough so cookies hold their shape and develop a better crumb; the kitchen will smell faintly of mint and butter as it rests. If chilled very cold, let the dough relax at room temperature so it scoops easily, because baking frozen dough can lead to uneven spread. A common pitfall is skipping chill time, which often causes excessive spreading; if time is tight, a short chill still helps, but be aware texture will differ from a fully rested dough.
When ready to bake, preheat oven to 350°F. Roll dough into balls or use a cookie scoop and line on a parchment lined baking sheet. Bake for 9-12 minutes or until cookies look slightly golden. When cookies come out of the oven, you can "pull them together" by putting a circle cookie cutter or biscuit cutter around each cookie and gently scoot them to form nice round cookies. Do not overbake your cookies–pull them out just before you think they are done.: As the oven warms, you will smell the chocolate blooming and the peppermint brightening. Watch the edges, which should set and turn a hint of gold while centers remain soft; this visual cue ensures tender centers. After removing them, the gentle nudge with a cookie cutter rounds the edges for a bakery look while the cookies are still warm and malleable. Avoid leaving them in until fully firm, because overbaking dries out the cookie and kills that soft chew everyone loves.
Allow to cool for several minutes before transferring to your mouth–er, a cooling rack.: Cooling is when texture finalizes, the edges crisp slightly and the center firms just enough to handle. The aroma will still rise in the cooling minutes, inviting a quick taste. Let them rest a few minutes on the pan, then move to a rack to avoid condensation that can make bottoms soggy. A typical error is transferring straight into an airtight container while too warm, which traps steam and softens the cookies, so always cool completely before storing.