Berry Squares

Preparation

1. Step 1

   Preheat oven to 350°F.

   Step 2

   Line a 9-inch square metal baking pan with a 12-inch-long sheet of foil, pressing it into bottom and up sides. Butter foil.

2. Make base and topping:

   Step 3

   Blend together oats, flour, brown sugar, zest, baking soda, and salt with your fingertips until well combined. Stir in butter. Reserve 3/4 cup of mixture for topping; transfer remainder to baking pan, pressing it firmly in bottom to form an even layer. Bake in middle of oven until golden, 12 to 15 minutes.

3. Make filling while base is baking:

   Step 4

   Stir together berries, sugar, juice, and ornstarch in a small saucepan, then bring to a boil over moderate heat. Cook, stirring, until thick and no longer cloudy, about 5 minutes, and remove from heat.

4. Assemble and bake squares:

   Step 5

   Spoon filling onto oat base, leaving a 1/2-inch border around edge. Crumble reserved oat mixture on top.

   Step 6

   Bake in middle of oven until golden and bubbly, 30 to 35 minutes. Cool completely in pan on a rack. Holding 2 ends of foil, lift from pan and put on a cutting board. Cut into 1 1/2-inch squares.