Preheat oven to 350°F (180°C). Line 2 baking sheets with parchment paper. Set aside.
Whisk flour and salt together in a medium bowl. Set aside.
Mix butter and sugar together in a large bowl until well combined. About 2 minutes of mixing.
Add in egg and vanilla extract and mix until well combined, scraping down the sides of the bowl as needed.
Add dry ingredients and mix until just combined. Scoop cookie batter out onto a large square of plastic wrap. Form into a rectangle, wrap it up, and store in the refrigerator for 1 hour or overnight.
After cookie dough has hardened, remove ⅓ of the dough and put the rest back in the refrigerator.
Roll dough on a lightly floured surface to½" thick. Use the large cross cookie cutter to cut out cookies. Place them on prepared baking sheets. Reroll up cookie dough until it's all used.
Use the small cross cookie cutter to cut out the middles of the cross. Place baking sheet in the refrigerator for 15 minutes to firm up before baking.
Remove baking sheet from the refrigerator. Add crushed up jolly ranchers to the cut out middles of the cross cookies. Try not to add too many, or the candy will overflow.
Bake for 8-10 minutes. If there is not enough candy coverage to the middle cross in the cookies, you can remove the baking tray partly through baking, and add more candy.
Remove baking sheets from the oven, and let the cookies get to room temperature on their baking sheets for at least 20 minutes before removing them.
Store cookies in an airtight container at room temperature for up to 5 days.