Combine all crepe ingredients, aside from butter, in a blender cup or mixer, and mix well. (You can also do it by hand, with a whisk.) Refrigerate for one hour.

Heat a seven- to eight-inch (18- to 20-centimeter) frying pan over medium heat. Smear with a little butter.

Pour one-fourth cup batter into the center of the pan. Lift and tilt pan to evenly coat bottom. Cook about 30–45 seconds, until the edges are starting to curl up. Turn out onto a large piece of paper towel. (These crepes are purposely thicker than the standard blintz leaves so they retain their shape when filled and baked.) Repeat with remaining batter, greasing frying pan as needed. Don’t stack the crepes until they’re fully cooled or they’ll stick together.

For the filling, cook potatoes in their peels in a pot of water until soft. Cool and peel with a knife.

Meanwhile, heat butter and olive oil in a large frying pan. Add onions and sauté until golden brown. Mash potatoes and mix together with onions, egg, salt and pepper, and parsley, if desired. Taste and adjust seasoning if necessary.

Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius).

Spray muffin tins with cooking spray. Press crepes gently in the pan with the edges sticking out.

Fill each crepe with a heaping tablespoon of the potato-onion mixture, pressing down gently. Top with about one teaspoon grated feta cheese.

Bake for 15 minutes. Cool in pans for five minutes and then carefully remove to a pan or plate.

Heat butter in a large frying pan.

Add garlic and sauté for one minute over low heat. Add mushrooms and seasonings and turn heat to medium. Stir until vegetables begin to soften, about five minutes.

Stir in cornstarch. Add lemon juice if desired. Add cooking cream and mix together until velvety and smooth.

Place a potato basket on a plate. Pour some cream sauce over the top.

Garnish with parsley.