Place potato in the microwave and cook on high until cooked through, about 7 minutes, depending on the size of the potato.

Split potato and remove flesh. Push flesh through a strainer using the back of a wooden spoon in order to achieve a granular texture. Add a pinch of salt and let cool for about 10 minutes.

Add beaten egg to potato and stir, using the tines of a fork and trying not to mash the potato. Add about 1/3 cup flour and continue to stir gently with the fork until mixture starts to come together. You may need another pinch or two of flour. Fold mixture with a spatula until dough forms a mass, adding flour as needed. Using your fingers, knead dough gently to form a ball, about 10 seconds.

Shape dough on a floured surface into a fat log. Cut log into four pieces. Gently roll each piece using your fingertips to form a 'snake' or a long rope of dough, starting from the center and rolling toward the end until dough is about 1/2-inch thick.

Cut each rope into 1/2-inch pieces, then roll each piece quickly down the back of a fork's tines to form ridges.

Heat marinara sauce in a skillet while you cook the gnocchi.

Bring a large pot of salted water to a boil. Reduce to a simmer and add gnocchi. As soon as they float to the surface (about 30 seconds or so), cook for an additional 14 seconds. Transfer with a slotted spoon to the pan with the sauce. Stir until coated.