Combine water, yeast and 1 teaspoon sugar in a small bowl; let stand for 5 minutes. Yeast mixture should be foamy. Combine warm milk, egg and butter in large mixer bowl. Add yeast mixture, 2-1/2 cups flour, sugar and salt. Beat for 2 minutes, scraping bowl occasionally. Add enough remaining flour to make a soft dough.
Knead on a lightly floured surface for 6 to 8 minutes, until dough is smooth and elastic. Place dough in a greased bowl, turning once to coat. Cover and let rise in a warm, draft-free place for 1 hour. Dough will not necessarily double.
Punch dough down. Divide dough in half. Roll each half into a 14 x 12-inch rectangle on a lightly floured surface. Place on a greased baking sheet. Spread 1/2 cup lemon curd in a 14 x 4-inch strip down center of the dough. Toss raspberries with corn starch and sprinkle half of the berries over the lemon curd.
Make 1-inch wide cuts with a sharp knife or scisssors on both sides of the dough, stopping about 1-inch before the filling . Fold each cut section of dough over the filling to resemble a braid. Repeat with second coffee cake. Cover and let rise 30 minutes.
Preheat oven to 350°F. Bake for 25 to 30 minutes, or until golden brown. Cool for 15 minutes on baking sheet before transferring to serving platter.
For glaze, combine powdered sugar, butter, vanilla and enough milk to reach desired consistency. Drizzle over warm coffee cakes.