Make 7 SunButter and jam sandwiches, spreading the SunButter and jam thickly. Cut off the crusts and cut each sandwich into 4 squares. Place in a greased 9-inch skillet or gratin pan in a single layer.
Whisk together the half-and-half, sugar, eggs, and vanilla. Pour over the mini sandwiches. Gently and lightly press the sandwiches down, making sure they get fully soaked in the cream mixture. Preheat the oven to 325 degrees and let the sandwiches soak while the oven preheats.
Bake for 45-50 minutes or until golden brown and the custard is set. Let sit for 5 minutes, then dust with powdered sugar and serve.