Cream together the brown sugar, butter, and vanilla until smooth and creamy, 1 to 2 minutes.
Add in cinnamon, flour, and salt and fold gently until dough just begins to come together. Turn it out onto a clean surface for rolling.
Press dough gently together until no more crumbs exist, then press into a square.
Lay a sheet parchment over the dough or use a lightly floured rolling pin to roll dough into a rectangle between 1/2" and 1/4" thick.
Slice the rectangle in half lengthwise, then cut lines widthwise every 1/2" creating many thin, long rectangles.
Shape each rectangle into a finger by pinching three times along its length. Once 1/2" in down, another 1/2" down, and a third time at the bottom of the rectangle.
Transfer to parchment lined baking sheet and repeat with remaining rectangles.
When fingers are all shaped, slice three small lines across the bumps created between the 1st and second pinch and the second and third pinches.
Slide a almond sliver into the dough at the tip of the finger. Cover and chill baking sheet for 30 minutes, up to 3 days.
Preheat oven to 350°F, take cookies out while oven preheats (About 10 minutes to allow the pan to warm slightly). Bake when oven is ready for 9 to 11 minutes or when bottom is just barely beginning to color.
Let cool on pan for 5 minutes then transfer to a cooling rack until completely cool.
Notes
*You can use granulated sugar instead of brown sugar if desired.*Add dye during the flour addition of mixing the dough to create green witch finger cookies.*Any nut can work as a fingernail if you don't have slivered almonds.*Store on the counter for 1 week in an airtight container.*If desired, add red jam to the fingernail and severed end for a more gruesome cookie. Then store in the fridge instead of the counter. OR, wait to add the jam until ready to serve.