I had a recipe I used for years (https://toriavey.com/challah-bread-part-1-the-blessing-and-the-dough/) which is lovely and sweet. She has excellent tips on braiding and re-egg-washing the white parts of the bread as it bakes. This is my current favorite from America's Test Kitchen. If you follow the instructions exactly you will have a beautiful loaf. BTW, I think American "all-purpose" flour is the same as your "plain" flour. It all comes down to the protein content. It's already Shabbos for most of you, so shabbat shalom and see you in the new week. My comments are in parentheses.
Easy-Braid Challah
Makes 1 Loaf
TIME 1¾ hours, plus 7 hours resting and cooling
GATHER YOUR INGREDIENTS
Flour Paste
½ cup water
3 tablespoons bread flour
Dough
1 large egg, plus 2 large yolks
¼ cup water
2 tablespoons vegetable oil
2 ¾ cups (15⅛ ounces/429 grams) bread flour (strong flour to you)
1 ¼ teaspoons instant or rapid-rise yeast
¼ cup (1¾ ounces/50 grams) granulated white sugar
1 teaspoon table salt
Vegetable oil spray
Egg Wash
1 large egg
Pinch table salt
1 tablespoon sesame seeds, or poppy seeds (optional)
BEFORE YOU BEGIN
This dough will be firmer and drier than most bread doughs, which makes it easy to braid. Some friction is necessary for rolling and braiding the ropes, so resist the urge to dust your counter with flour. If your counter is too narrow to stretch the ropes, slightly bend the pieces at the 12 o'clock and 6 o'clock positions. Bake this loaf on two nested baking sheets to keep the bottom of the loaf from getting too dark.
2
For the flour paste: Whisk water and flour in bowl until no lumps remain. Microwave, whisking every 20 seconds, until mixture thickens to stiff, smooth, pudding-like consistency that forms mound when dropped from end of whisk into bowl, 40 to 80 seconds. (Don't skip. This is an important step.)
3
For the dough: In bowl of stand mixer, whisk flour paste, egg and yolks, water, and oil until well combined. Add flour and yeast. Fit mixer with dough hook and mix on low speed until all flour is moistened, 3 to 4 minutes. Let stand for 20 minutes. (Also important. This step allows the flour to absorb the liquids.)
4
Add sugar and salt and mix on medium speed for 9 minutes (dough will be quite firm and dry). Transfer dough to counter and lightly spray now-empty mixer bowl with oil spray. Knead dough briefly to form ball and return it to prepared bowl. Lightly spray dough with oil spray and cover bowl with plastic wrap. Let dough rise until about doubled in volume, about 1½ hours.
5
Line rimmed baking sheet with parchment paper and nest in second rimmed baking sheet. Transfer dough to counter and press into 8-inch square, expelling as much air as possible. Cut dough in half lengthwise to form 2 rectangles. Cut each rectangle in half lengthwise to form 4 equal strips of dough. Roll 1 strip of dough into 16-inch rope. Continue rolling, tapering ends, until rope is 18 inches long. Repeat with remaining dough strips. Arrange ropes in plus-sign shape, with 4 ends overlapping in center by ½ inch. Firmly press center of cross into counter to seal ropes to each other and to counter.
6
Lift rope at 12 o'clock, bring over center, and place in 5 o'clock position. Lift rope at 6 o'clock, bring over center, and place in 12 o'clock position.
7
Lift rope at 9 o'clock, bring over center, and place in 4 o'clock position. Lift rope at 3 o'clock and, working toward yourself, bring over braid and place in 8 o'clock position. Adjust ropes so they are at 12, 3, 6, and 9 o'clock positions.
8
Repeat steps 5 and 6, working toward yourself, until you can no longer braid. Loaf will naturally list to 1 side.
9
Pinch ends of ropes together and tuck both ends under braid. Carefully transfer braid to prepared sheets. Cover loosely with plastic and let rise until dough does not spring back fully when gently pressed with your knuckle, about 3 hours.
10
For the egg wash: Thirty minutes before baking, adjust oven rack to middle position and heat oven to 350F (175C) degrees. Whisk together egg and salt. Brush loaf (VERY THOROUGHLY) with egg wash and sprinkle with seeds, if using. Bake until loaf is deep golden brown and registers at least 195F (90C) degrees, 35 to 40 minutes. Let cool on sheets for 20 minutes. Transfer loaf to wire rack and let cool completely before slicing, about 2 hours.