a small heart-shaped cookie cutter with straight edges
Line a loaf pan with plastic wrap, leaving excess on all sides to fold over the top. In a medium bowl, combine the sprinkles and 1/2 cup of crumbs from the Heart-Shaped Blondies. Set aside.
Soften 1/2 cup of the ice cream and spread in an even layer on the bottom of the loaf pan. Freeze the layer of ice cream until set, about 30 minutes.
Meanwhile, place the 12 heart-shaped blondies in a row and press them together as tightly as possible.
Soften all of the remaining ice cream until smooth and easy to spread. Remove the loaf pan from the freezer and spread another 1/2 cup of softened ice cream over the bottom. Carefully place the log of blondies, heart lobes down against the ice cream, in the center of the pan. There should be a 1/2-inch gap between both ends of the log and the ends of the loaf pan.
Spread the remaining softened ice cream around the log, filling the loaf pan to the top. Work carefully to keep the blondies pressed together tightly. Top the loaf with the blondie crumb/sprinkle mixture in an even layer. Fold the plastic wrap over the cake. Freeze until set, about 4 hours.
Invert the pan to remove the ice cream cake. Peel off the plastic wrap and discard. Slice the ice cream cake like a loaf of bread, revealing the hidden heart inside. Serve immediately.
Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper.
In a small saucepan, melt the butter. Put the sugar in a large bowl, add the butter and stir to combine. Cool to room temperature. Beat in the red food coloring, vanilla and eggs.
In a medium bowl, whisk together the flour, baking powder and salt. Add the flour mixture to the wet ingredients, mixing just until a smooth batter is formed.
Transfer the batter to the prepared baking sheet and spread into an even layer. Lay another sheet of parchment paper over the batter and place an inverted baking sheet over the top. Bake until a toothpick inserted in the center comes out clean, about 20 minutes. Cool the blondies in the baking sheet slightly before inverting them onto a cooling rack. Cool completely.
Cut the blondies into 12 hearts using a small heart-shaped cookie cutter with straight edges. The hearts should be about 1/2 inch thick. Crumble the remaining blondies into coarse crumbs.