Butter the sides of a 6-quart slow cooker. Sprinkle with granulated sugar. Turn over to remove any excess sugar.
In a small saucepan heat half-and-half and vanilla bean until bubbles form at edge of saucepan. Remove from heat. Remove vanilla bean; let cool for 5 minutes. Using a paring knife, split vanilla bean lengthwise. Scrape out seeds. Stir seeds into half-in-half.
In another small saucepan melt the 1/4 cup butter. Stir in flour. Add half-and-half mixture. Cook over medium heat until thickened and bubbly, whisking constantly. Remove from heat (mixture will be thick). Gradually whisk into the egg yolks; set aside. Let cool about 30 minutes.
Meanwhile, in a bowl combine fruit and the 3 tablespoons sugar. Cover and chill until ready to serve.
In a bowl beat egg whites and vanilla with a mixer on medium speed until soft peaks form (tips curl). Gradually add the 1/2 cup sugar, 1 tablespoon at a time, beating on medium-high until stiff peaks form (tips stand straight). Fold about 2 cups of the egg white mixture into the egg yolk mixture to lighten. Gently fold the egg yolk mixture into the egg white mixture until combined. Spoon into the prepared cooker.
Cover and cook on high for 1 1/4 to 1 1/2 hours or until a knife inserted into the center comes out clean. Dust with powdered sugar. Serve immediately with fruit.