In the bowl of a stand mixer fitted with the paddle attachment, beat together 1 cup flour, sugar, yeast, and salt at low speed until combined.
In a small saucepan, heat together evaporated milk, butter, and 2 tablespoons plus 2 teaspoons water over medium heat until mixture registers 120° to 130° on a candy thermometer. With mixer at low speed, add hot milk mixture to flour mixture. Increase mixer speed to medium, and beat for 2 minutes. Add egg and ½ cup flour; beat at high speed for 2 minutes. Gradually add remaining ½ cup flour, beating until a soft dough forms.
Switch to the dough hook attachment; beat at medium speed until dough is smooth but still sticky, approximately 5 minutes. Turn out dough onto a lightly floured surface, and knead until very soft, smooth, and no longer sticky, approximately 1 minute. If dough seems too sticky, add 2 tablespoons more flour. (Dough should be on the soft side, so don’t add too much flour, or conchas won’t be as soft.)
Spray a large bowl with cooking spray. Place dough in bowl, turning to grease top. Cover with plastic wrap, and let rise in a warm (75°), draft-free place until doubled in size, 1 to 1½ hours.
Line 2 baking sheets with parchment paper.
Punch down dough, and turn out onto a lightly floured surface. Divide dough into 15 equal portions, and shape each portion into a smooth ball. Flatten each ball into a 2¼-inch disk, and place on prepared pans. Top each dough ball with an Egg Streusel Topping patty. Using a small paring knife, carefully cut a design (vertical lines to resemble a shell pattern or crisscross lines) into streusel, leaving a ¼-inch border. Let rise in a warm (75°), draft-free place until almost doubled in size, 45 to 60 minutes.
Preheat oven to 375°.
Bake until topping is just beginning to brown, 15 to 20 minutes. Serve warm or at room temperature. Store in an airtight container at room temperature for up to 2 days.
Recipe by TeaTime Magazine at https://teatimemagazine.com/conchas-mexican-sweet-rolls/