Heat oven to 400°F. Grease bottom and sides of 9x9-inch pan with shortening.

In saucepan, cook filling ingredients over low heat about 10 minutes, stirring constantly, until thickened. Cool 5 minutes. Or microwave for 6 mins on 60% (I used stick blender a little.)

In large bowl, stir brown sugar and butter until well mixed. Stir baking soda into flour, then into butter mixture along with oats until crumbly. Press half of the crumb mixture evenly in bottom of pan. Spread with filling. Top with remaining crumb mixture; press lightly.

Bake 25 to 30 minutes or until light brown. Cool 5 minutes in pan on cooling rack. Cut into 4 rows by 4 rows while warm.