Spray a 13x9-inch baking pan with baking spray with flour.

In a large bowl, whisk together semolina, salt, baking powder, baking soda, and cinnamon.

In a medium bowl, whisk together milk, sugar, yogurt, and vanilla. Add milk mixture to semolina mixture, and whisk until well combined. Spread batter into prepared pan. Cover and refrigerate for 30 minutes.

Preheat oven to 350°F (180°C).

Bake, uncovered, until a wooden pick inserted in center comes out clean and an instant-read thermometer inserted in center registers 205°F (96°C), 18 to 25 minutes. Immediately spoon Cinnamon Simple Syrup evenly onto hot cake. Let cool completely in pan on a wire rack.

Spread Crème Diplomate onto cooled cake. Cover and refrigerate for at least 4 hours before serving or up to overnight. Just before serving, garnish with cinnamon, if desired. Cover and refrigerate for up to 3 days.