Notes: Buy ice cream in cardboard cartons, not plastic tubs (you need to be able to snip the cartons and peel them off, then quickly slice the ice cream). It's easiest to use ice cream in rectangular cartons, but round ones will work.
About 1/3 cup butter or margarine
1/2 cup firmly packed brown sugar
1/4 cup dark corn syrup
1 teaspoon vanilla
1/4 teaspoon salt
2 cups quick-cooking rolled oats
1/2 cup sweetened shredded dried coconut or sliced almonds
1 quart strawberry or peach ice cream
How to Make It
Lightly butter a 10- by 15-inch rimmed baking pan. Line pan with a 15- by 20-inch piece of cooking parchment, spreading it smooth (edges will stick up above pan rim). Butter and flour parchment.
In a 2- to 3-quart pan over medium-high heat, melt 1/3 cup butter, stirring often, about 2 minutes. Remove from heat and add sugar, corn syrup, vanilla, and salt; stir until smooth. Add oats and coconut; mix until evenly blended. Scatter oat mixture in lined pan; with a long metal spatula, spread mixture level.
Bake in a 375° regular or convection oven until cookie is browned at edges and bubbling all over, about 10 minutes. Let cool just until cookie begins to firm but is still warm, about 2 minutes (if too cool, cookies will crack when cut). Invert a 12- by 15-inch baking sheet over pan; holding pan and sheet together, carefully invert cookie onto sheet. Cut into 18 rectangles 2 1/2 by 3 1/3 inches. Let cool.
Return 9 of the cookies, smooth side up, to lined pan, setting them side by side in a single layer to make a snug rectangle in half the pan.
With scissors, snip through opposite sides of ice cream carton from top to bottom; peel carton from ice cream and discard. Working quickly, place ice cream on a board (if round, trim off 1 side and lay on flat side). With a long, heavy knife, cut crosswise into 1/2-inch-thick slices. Set slices side by side over cookies in pan; fill in any bare spots with ice cream scraps to cover completely, and trim off any excess. Freeze remaining ice cream for other uses. Cover ice cream with remaining 9 cookies, matching the orientation of bottom cookies. Wrap pan airtight and freeze until ice cream is firm, at least 3 hours.
Lift ice cream sandwiches on parchment from pan and transfer to a board. Cut between cookies; trim sandwich edges with a knife, if desired. Serve, or wrap sandwiches individually airtight and freeze up to 2 weeks.