- HEAT oven to 350°F. In larger bowl, beat butter and sugar until light and fluffy. Add eggs, vanilla and instant coffee, if desired; beat well.
- COMBINE oats, flour, baking soda, salt and 1 cup walnuts; gradually add to creamed mixture. (Dough will be stiff; stir in last part by hand.) Reserve 2 cups dough.
- PRESS remaining dough evenly on bottom of 15×10-inch baking pan with floured hands. Spread Chocolate Filling evenly over dough in pan. Crumble reserved dough over chocolate. Sprinkle remaining 1/2 cup walnuts over top.
- BAKE 25 minutes or until top is golden (chocolate will be soft). Cool completely. Cut into bars. Store leftovers covered at room temperature.
- Chocolate Filling: In heavy saucepan, over low heat, melt butter. Stir in cocoa. Add sweetened condensed milk; cook, stirring constantly, until smooth and thick. Remove from heat. Stir in vanilla.