In a bowl, dissolve yeast in warm water. Stir in flour, cover with plastic wrap and set in a warm place until foamy, about 10 minutes. (I like to place on the stove under the light).
For the dough:
In the bowl of an electric mixer, combine 2 cups flour, sugar and salt; whisk by hand until well blended. Transfer bowl to mixer and attach dough hook. With mixer on low speed, add egg and milk. Increase speed to medium and knead 5 minutes. Add butter and knead 5 minutes. Stop mixer and add sponge. continue kneading on medium speed until dough is smooth and elastic, 7 to 8 minutes, adding more flour if needed. Cover the bowl with a towel and let rise in a warm place until doubled, about 1 hour.
Butter 12 cupcake molds. Punch down dough, transfer to a lightly floured surface and knead in chocolate chips. Divide dough into 12 equal parts.
Roll on the table in a circular motion to give body to the brioche. With your finger, "saw" a small piece of the brioche in a back and forward motion. This forms a small lump which should remain attached to the body of the brioche.
Place the brioches into the buttered molds.and let rise in a warm place 45 minutes.
Brush tops of brioches with egg mixture. Bake until golden brown, 15 to 20 minutes. Remove from molds and let cool completely. Store brioches in a plastic bag to avoid drying out
The first recorded use of the word "brioche" in French dates back to 1404. In 1611, Cotgrave's A Dictionarie of the French and English Tongues, described brioche as "a rowle, or bunne, of spiced bread" stated its origin as Norman.
In France it developed as "a sort of bread improved since antiquity by generations of bakers, then of pastry-makers ... with some butter, some eggs, sugar coming later ... it developed from the blessed bread [pain bénit] of the church which gradually became of better quality, more and more costly, less and less bread; until becoming savoury brioche".