Heat oven to 350°F. Spray bottom of 13x9-inch pan with baking spray with flour. In large bowl, beat butter and brown sugar with electric mixer on medium speed until fluffy. Add eggs; beat on medium-high speed until fluffy. Add flour, baking powder and salt; beat on low speed until mixed.
With spoon, stir in white chocolate and 3/4 cup of the cashews until well mixed. Spread in pan. Sprinkle with remaining 1/2 cup cashews; press down lightly.
Bake 25 to 30 minutes or until edges look dry, center is set and toothpick inserted 2 inches from edge of pan comes out clean. Cool completely, about 1 hour. For bars, cut into 8 rows by 4 rows.