1Line 8x4-inch loaf pan with plastic wrap, leaving edges hanging over sides of pan. Divide evaporated milk evenly between 2 small bowls. Stir Boston cream pie yogurt into one bowl; stir red velvet yogurt into remaining bowl. Cover and refrigerate red velvet yogurt mixture.
2Spread Boston cream pie mixture into lined pan. Sprinkle with crushed crisps. Freeze 2 hours. Spoon and spread red velvet yogurt mixture on top. Freeze at least 2 hours until firm.
3When ready to serve, dip bottom half of pan into hot water about 1 minute to loosen yogurt mixture. Use plastic wrap to lift frozen yogurt from pan. Pull back wrap and remove. Let stand 5 to 10 minutes to soften slightly. Cut into eight 1-inch-thick slices. Serve immediately.