Peel 2 large Russet potatoes and cut into 1-inch chunks.
Place potato chunks in a pot, cover with cold water by 1 inch, add 1 teaspoon salt, bring to a boil, then simmer until fork-tender, about 15–20 minutes.
Drain potatoes thoroughly and return to the hot pot, let steam dry for 1–2 minutes, then mash until smooth.
Stir 2 tablespoons cornstarch into the mashed potatoes until a thick dough forms.
Transfer mashed potato mixture to a bowl, cover, and refrigerate for at least 30 minutes.
Lightly flour a work surface, roll out half of the chilled potato dough to 1/4-inch thickness, and cut 2-inch circles.
Use a straw to punch two eye holes and a knife or spoon edge to carve a smile on each circle; place shapes on a parchment-lined baking sheet.
Freeze the shaped smiley fries on the baking sheet for at least 1 hour, until firm.
Heat 4 cups vegetable oil in a heavy-bottomed pot to 350°F (175°C).
Fry a few frozen smiley fries at a time for 3–5 minutes per side, until golden brown and crispy.
Drain fries on paper towels and immediately sprinkle with additional salt to taste.
Serve warm with your favorite dipping sauces.