Dissolve yeast in warm water in large bowl.
Add all-purpose flour, 1/4 cup butter, the sugar, salt and 2 eggs.
Beat on low speed until moistened.
Beat on medium speed, scraping bowl occasionally, 3 minutes.
Stir in enough of the whole wheat flour to make dough easy to handle.
Turn dough onto lightly floured surface; knead until smooth and elastic, about 5 minutes.
Place in greased bowl; turn greased side up.
Cover; let rise in warm place until double, about 1 hour.
Punch down dough; refrigerate 1 hour.
Punch down dough; roll into rectangle, 25 x 10 inches.
Spread with 1/3 cup of the butter.
Fold rectangle crosswise into thirds, overlapping 10-inch edges to make 3 layers; roll into rectangle, 25 X 10 inches.
Spread with 1/3 cup of the butter.
Fold into thirds; roll into rectangle, 25 x 10 inches.
Spread with remaining 1/3 cup butter.
Fold into thirds (do not roll into rectangle).
Cut dough into halves; refrigerate 1 hour.
Roll one half into rectangle, 18 x 12 inches.
Cut lengthwise into halves; then cut crosswise into 3 squares.
Cut each square diagonally into 2 triangles.
Flatten triangles slightly with rolling pin.
Roll up each triangle, beginning at long side.
Place rolls, with points underneath, on greased cookie sheet; curve to form crescents.
Cover; let rise at room temperature about 1 hour.
Heat oven to 425°.
Brush croissants with beaten egg.
Bake until croissants are brown and crisp, 14 to 16 minutes.
Chocolate-filled Croissants: Place 1 teaspoon chocolate chips at the long side of each triangle before rolling.
Hazelnut-filled Croissants: Mix 1/2 cup finely chopped hazelnuts, 2 tablespoons sugar, 14 teaspoon vanilla and 1 egg.
Spread each triangle with 1 heaping teaspoon.
Traditional Croissants: Substitute all-purpose flour for the whole wheat flour.