1. Preheat oven to 350°. Lightly grease a 9-inch springform pan, and dust with flour. Wrap outside of pan halfway up sides with aluminum foil, and place in a heavy-duty roasting pan.
2. Combine first 5 ingredients in a small saucepan, and bring to a simmer over medium heat. Slowly whisk in semolina flour until smooth. Remove from heat, and place in a large bowl to cool. Add butter and pumpkin, stirring well.
3. Sift together all-purpose flour, baking powder, and salt in a medium bowl; fold into pumpkin mixture until incorporated.
4. Beat egg yolks and 1/2 cup sugar at medium speed with an electric mixer until light yellow and fluffy, about 3 minutes. Clean mixer blades, and beat egg whites in a separate bowl at high speed with an electric mixer until frothy. Gradually add remaining 1/4 cup sugar, and beat to form stiff peaks. Fold yolk mixture into pumpkin mixture; gently fold in egg whites.
5. Pour batter into prepared pan, place in a water bath, and bake at 350° for 50 to 55 minutes or until set in the center.
*Available in most supermarkets, semolina flour is made of wheat that's ground more coarsely than regular flour.