Instructions

for the doughnuts

Whisk flour, sugar, yeast, and salt together in bowl of stand mixer. Lightly beat milk and egg together in separate bowl, then add to flour mixture. Fit stand mixer with dough hook and mix on low speed until all ingredients are moistened, about 30 seconds. Increase speed to medium and continue to mix until sticky dough just forms, 2 to 3 minutes, scraping down sides of bowl as needed.
With mixer running, add butter and continue to mix until fully incorporated and dough is smooth and elastic and clears sides of bowl, about 15 minutes, scraping down bowl halfway through mixing. Transfer dough to lightly greased large bowl. Cover with plastic wrap and let sit at room temperature until doubled in volume, about 30 minutes. Clean and dry mixer bowl and place it in freezer.
Transfer dough to lightly floured counter and gently press it into 10-inch square of even thickness. Fold dough into thirds, like business letter. Using bench scraper or sharp knife, cut rectangle in half lengthwise, then cut each strip into 5 equal pieces (about 67 grams each). Working with 1 piece of dough at time, form it into rough ball by stretching dough around your thumb and pinching edges together so that top is smooth. Place ball seam side down on clean counter and, using your cupped hand, drag it in small circles until dough feels taut and round. Pinch bottom seam to ensure it's sealed securely and cover with plastic. Let dough balls rest for 20 minutes.
Cut ten 4-inch square pieces of parchment paper, arrange on two rimmed baking sheets, and lightly spray with vegetable oil spray. Working with 1 piece of dough at time, gently flatten it with your hand to expel air, then reshape into smooth, taut ball. Pinch bottom seam to seal. Using small greased rolling pin, press and roll dough ball into 3-inch round. Arrange dough rounds seam side down on prepared parchment squares. Bring 1 quart water to boil.
Adjust oven racks to upper-middle and lower-middle positions. Place shallow baking pan on bottom of oven. Preheat oven to 200 degrees for 1 minute, then turn off oven. Pour boiling water into prepared pan. Place sheets on racks, close oven, and allow doughnuts to rise until doubled in size, about 30 minutes. Remove doughnuts from oven and let sit for 5 minutes to allow their surface to dry.
About 20 minutes before end of rising time, following manufacturer's instructions, heat oil in electric fryer to 350 degrees. Working with 1 doughnut at time, lift it from baking sheet along with parchment square. Using edge of parchment to assist you, carefully flip and lower doughnut into hot oil, then peel away and discard parchment. Repeat with 4 more doughnuts. Cook doughnuts until golden brown on undersides, about 90 seconds. Using spider skimmer, flip doughnuts and cook until second sides are browned, about 90 seconds. Transfer doughnuts to prepared rack. Return oil to 350 degrees and repeat with remaining 5 doughnuts. Let doughnuts cool completely, about 30 minutes.

for the filling

Using stand mixer fitted with chilled bowl and whisk attachment, whip cream and sugar on medium-low speed until foamy, about 1 minute. Increase speed to medium and whip until stiff peaks form, 8 to 9 minutes.
Using serrated knife, cut each doughnut in half horizontally, stopping about ½ inch before edge. Working with 1 doughnut at time, open halves, being careful to leave uncut section intact, and spread 6 grams (1 teaspoon) condensed milk over bottom half. Spoon rounded ½ cup whipped cream onto bottom half, then fold over top half. Gently press halves together until whipped cream extends just beyond cut edges of doughnut. (Doughnut should still be quite open.) Using offset spatula, spread whipped cream to fill in any gaps in opening and create smooth surface. Clean edges of doughnut, then press 4 or 5 strawberry slices, if using, into whipped cream to create decorative border. Dust tops of doughnuts with confectioners' sugar and serve.