Dissolve yeast in warm water in bowl; stir in 1/2 teaspoon sugar. Add 2 cups flour, 1/4 cup sugar, 3/4 cup butter, sour cream, egg yolks, salt, almond flavoring and vanilla. Beat at medium speed, scraping bowl often, until smooth.
Stir in enough remaining flour to make dough easy to handle. Turn dough onto well-floured surface; knead 8-10 minutes or until smooth and elastic. Place into greased bowl; turn, greased-side up. Cover; let rise in warm place about 1 1/2 hours or until double in size. (Dough is ready if indentation remains when touched.)
Combine currants and candied fruit mix in bowl. Pour brandy over fruit; let stand 15 minutes.
Punch down dough. Place dough onto lightly floured surface. Knead fruit and brandy mixture into dough just until fruit is thoroughly distributed. Roll out dough on lightly floured surface to 14x10-inch oval, approximately 1/2-inch thick.
Stir together almond paste and 3 tablespoons butter in bowl. Spread mixture lengthwise on dough. Fold oval lengthwise so top edge is within 1 inch from bottom edge. Pinch edges gently to seal. Place onto greased baking sheet. Cover; let rise 45 minutes. (Stollen will not double in size.)
Heat oven to 350°F.
Combine 1 egg and milk in bowl; beat with fork. Brush onto stollen. Bake 35-45 minutes or until golden brown. Cool completely.
Sift powdered sugar over top of stollen.