Microwave the butter for about 40 seconds. Butter should be completely melted but shouldn't be hot.
In a large bowl, mix butter with the sugars until well-combined.
Stir in vanilla and egg until incorporated.
Add the flour, baking soda, and salt. Mix until just combined. Dough should be soft and a little sticky but not overly sticky.
Gently fold in sprinkles
Scoop out 1.5 tablespoons of dough (medium cookie scoop) and place on baking sheet.
Bake for 7-10 minutes, or until cookies are set. They will be puffy and still look a little underbaked in the middle.
Video
[adthrive-in-post-video-player video-id="I3JXZQ1q" upload-date="2020-08-20T19:26:12.000Z" name="Funfetti Cookie.mp4" description="Easy homemade funfetti cookies are sprinkle vanilla butter cookies with soft middles and chewy edges. No cake mix, mixer, or chilling necessary to make these fun cookies." player-type="default" override-embed="default"]
Notes
Sprinkles: Betty Crocker Rainbow Sprinkles work well because they don't bleed.
Baking: Don't overbake or the cookies won't be soft.