Carefully remove the cooled polenta from the baking dish and place on a cutting board. Use a butter knife and gently release the polenta from the edge of the dish if needed.
Slice a strip about 4 inches wide and 8 inches long. Cut that strip in ½ to make 4x4 inch squares. Cut the squares in ½ on the diagonal to make a triangle.
Carefully coat the top and bottom of the polenta triangles in flour. Try not to get the sides of the polenta covered in flour.
Preheat olive oil in a frying pan or cast iron skillet over medium heat.
While the polenta is frying, start the mushroom sauce.
Once the oil is hot, add the polenta triangles, bottom side in the oil. Cook 5 minutes or until golden brown and releases easily from the pan. Flip the polenta triangle over and cook the top side for 4-5 minutes or until golden brown and crispy.
Remove from pan and set on a cooling rack over a baking sheet (this will keep the polenta crispy) season with salt.