Preheat oven to 375 degrees.
In a mixing bowl, combine butter and sugars and mix until smooth.
Add in vanilla and eggs and mix until blended.
Add in 1 1/4 cups flour, sprinkle salt and baking soda over-top and mix until smooth.
Divide dough in half. add remaining 1/2 cup of flour to one half and mix until blended.
Add the cocoa powder to the other half and mix until blended.
Scoop the "vanilla" dough into balls using a small cookie scoop (fill scoop a little less than full) and place on a piece of parchment paper.
Do the same with the chocolate dough.
Take one of each, press them together, flatten them down into a fat disk and roll edges liberally in the chocolate jimmies.
Place onto a parchment paper lined lined baking sheet, one inch apart (I usually fit 7 per sheet).
Bake 11 minutes or so or until done to your liking. You don't want edges to brown.
Allow them to cool on tray for a couple minutes and then using a cookie spatula, transfer them to a cooling rack until completely cool.
Store in a cookie jar or airtight container and enjoy!