Preheat oven to 400 degrees. Grease the baking sheet. Roll out puff pastry to 1/4 inch thick. Cut into 2 pieces. Place 1 sheet on baking sheet. Heat olive oil and saute onions until golden brown. Add potatoes and stir for 3 minutes. Add garlic. Season with marjoram, salt and pepper. Remove from heat and allow to cool to room temperature. Spread mixture on pastry bottom leaving 1 inch border. Brush edges with egg. Cover with other pastry piece and brush with remaining egg. Bake for 15 minutes. Remove from oven and cool for 5 minutes. Cut a 1 inch slit into the strudel and pour in half and half. Lower oven temp to 200 degrees and bake for another 10 minutes. Remove and serve.