In a standing mixer, add the starter, flour, salt, yeast, and shortening (melted and cooled to below 115˚F / 46˚C).
Turn on the mixer and begin kneading, slowly add the water and continue to knead on low speed.
Knead for 10 minutes or until the dough pulls away from the bowl.
Scoop the dough out onto a floured surface, deflate it, and shape it into a ball.
Spray a large bowl (mixer bowl is fine) with cooking spray, place the dough in the bowl, spray the top of the dough with cooking spray and cover the bowl with plastic.
Place the covered bowl in a warm space and allow the dough to rise for about 1½ hours or until it is doubled in size.
Deflate the dough and scoop it out onto a floured surface. Divide the dough into 10 equal pieces. You can use a food scale or eyeball the divisions. Depending on the overall weight of your dough, the individual pieces should weigh 3-4 ounces.
Cover the 10 pieces on the work surface with sprayed plastic wrap and let the dough rest for 15 minutes.
Form the Bolillos by flouring your hands, flatten each piece of dough with the palm of your hand. Fold ⅓ of dough over and press down with your fingers pinching the fold against the flat portion of the dough to seal it, Then, continue to fold the dough over to the edge pinching the fold to the edge of the dough. Be sure to seal the ends of the roll.
Shape the Bolillos into footballs, place your hands over the dough and press gently but firmly cupping your hands and rolling back and forth. While doing this, press the edges of your hands to leave some dough uncovered to form the traditional Bolillo ears or tapered ends of a football.
Place each Bolillo seam side down on a parchment-lined baking sheet or greased baking sheet and cover with sprayed plastic wrap. Allow them to rise for 1 to 1½ hours or until they’ve doubled in size.
With 15 minutes left in the rising process, set your oven to preheat at 450˚F / 232˚C. Place a metal pan on the lowest rack level in your oven.
When the rolls have doubled in size, make a deep cut using a serrated knife in the center of the roll in the direction from tail to tail.
Spray the rolls with warm water or use your fingers and spritz them with the water.
Place the rolls in the oven, pour 1½ cups of cold water in the metal pan, and immediately close the oven. The cold water hitting the heat will result in steam causing a crunchy crust.
Bake for 20-25 minutes until the rolls are golden brown. Remove them from the oven and allow them to cool. Eat and enjoy!