Prepare filling: Place strawberries in a heavy saucepan and stir continuously over medium-low heat until juices are released from the berries. Bring strawberries to a boil over medium-high heat. Add sugar, stirring to combine. Use a wooden spoon to crush and mash the strawberries for a smooth texture. Sir in lemon juice. Continue cooking until the mixture thickens, slowly bubbles, and coats the back of the spoon. Pour the filling into a clean glass bowl and press a piece of plastic wrap directly on the surface. Refrigerate filling overnight until completely chilled.
Prepare dough: Combine 2 cups (280 g) flour, yeast, sugar, and salt in a large mixer bowl; mix on low speed until incorporated. Heat milk in a microwave-safe measuring cup for 45 seconds to 1 minute, until very warm (120-130°F).
Add warm milk, butter, and egg to flour mixture and mix until combined; mix in remaining 1 ½ cups (210 g) flour. Switch out the flat beater for a dough hook, and knead dough for 3 minutes until smooth and elastic. The dough is ready when it feels tacky but doesn’t stick to your fingers.
Place dough in a large bowl coated with nonstick spray and cover with plastic. Let the dough rise in a warm place until doubled in size, about 45 minutes. To check if dough has doubled, lightly flour two fingers and press them down into center of dough. If indentations remain, gently press down dough; cover and let rest 5 minutes.
Turn dough out on a lightly floured board and divide into four equal pieces. Shape each piece into a ball, and let rest for 5 minutes.
Roll one piece of dough out into a 10-inch circle and transfer to a parchment-lined baking sheet. Spread with softened butter, leaving a ¼-inch border. Spread approximately 2 ½ tablespoons strawberry filling spread over the dough, leaving a ½-inch border.
Roll out the second piece of dough into a 10-inch circle, and stack on top of the first piece of dough. Spread with softened butter and strawberry filling, leaving a ½-inch border. Repeat process with remaining dough, leaving the top circle bare.
Transfer baking sheet to the freezer and freeze the assembled bread for 20 minutes.
Place a 2-inch round cutter in the center of the dough; press gently to leave an imprint. Use a sharp knife to cut the circle into 4 equal sections, from the imprint in the center to the edge, cutting through all the layers. Wipe knife clean and cut each section into 4 equal strips, for a total of 16 strips.
Using both hands, pick up 2 adjacent dough strips and twist them away from each other twice. Pinch the ends of the strips together firmly. Repeat with remaining strips of dough, for a total of 8 points. Cover the star loosely with plastic and let rise in a warm place until puffy, about 25 minutes. While the star rises, preheat oven to 375°F.
Brush dough gently with melted butter and sprinkle with sugar. Bake for 25 to 30 minutes, or until golden and the internal temperature reaches 200°F.
Remove star bread from oven and place on a wire rack to cool for 20 minutes. Dust with powdered sugar and serve with remaining strawberry filling.
Notes
Strawberry filling can be made ahead and chilled for 1-2 days.