Stir together flour, KELLOGG'S ALL-BRAN cereal, soda and salt. Set aside.
In large mixing bowl, beat shortening, brown sugar and vanilla until light and fluffy. Add egg. Beat well. Combine milk and lemon juice. Add flour mixture alternately with milk. Drop by heaping tablespoon, 4 inches apart, onto baking sheets coated with cooking spray. Spread dough to make an even round cookie, 1/4-inch thick and 2-inches in diameter..
Bake at 400° F about 5 minutes or just until cookies are golden but still soft. Do not overbake. Remove from baking sheet and cool completely on wire racks.
Spread about 1/3 cup ice cream on bottom side of each 10 cookies, top with remaining cookies to make sandwiches. Freeze at least 1 hour before serving. Sandwiches may be wrapped in foil or plastic wrap and placed in airtight container for storage in freezer. Yield: 10 sandwiches