1. Heat oven to 350°F. Grease 9-inch square baking pan.
2. Stir together apples, 3/4 cup sugar, and 1/4 cup flour in large bowl. Spread in prepared pan; dot with 2 tablespoons butter. Combine oats, remaining 3/4 cup flour, remaining 1/4 cup sugar and cinnamon in medium bowl; set aside.
3. Place remaining 1 tablespoon butter and peanut butter in small microwave-safe bowl. Microwave at MEDIUM (50%) 30 seconds or until butter is melted; stir until smooth. Add to oat mixture; blend until crumbs are formed. Sprinkle crumb mixture over apples.
4. Bake 40 to 45 minutes or until apples are tender and edges are bubbly. Cool slightly. Serve warm or cool with whipped cream or ice cream, if desired. 6 to 8 servings.