In the bowl of a stand mixer fitted with the dough hook, combine flour, sugar, lemon zest, yeast, and salt.
Heat butter and milk in a small saucepan over low heat, stirring occasionally, until butter melts.
Cool to 120℉.
Pour over dry ingredients.
Mix at low speed until ingredients are just combined.
Add eggs.
Mix at low speed until incorporated.
Increase speed to medium.
Knead dough until smooth and elastic (it will clean the sides and bottom of the bowl when done), about 5-8 minutes.
Place dough in a lidded container that has been sprayed with cooking spray, or in a glass bowl covered with plastic wrap.
Let rise in a warm place until doubled in bulk, about 1-1½ hours. You can also use a proofing box with a humidity tray set to 78℉, and leave the plastic wrap off.
While dough is proofing, make the lemon sugar and the blueberry syrup.