01 - Combine milk, water, butter, and salt in a saucepan. Bring to a boil over medium-high heat. Reduce heat to low and add flour all at once, stirring vigorously with a wooden spoon until dough forms and pulls away from sides of pan. Remove from heat and let cool for 5 minutes. Transfer to a lightly floured surface and knead until smooth, about 2-3 minutes. Cover with plastic wrap and set aside.
02 - Bring a pot of salted water to simmer. Add shrimp and cook for 2-3 minutes until pink and opaque. Drain thoroughly, let cool, then chop into small pieces. Set aside.
03 - Melt butter in a skillet over medium heat. Add onion and sauté until translucent, about 4 minutes. Add garlic and cook 1 more minute. Sprinkle flour over mixture and stir constantly for 1-2 minutes to cook out raw taste. Gradually whisk in milk, stirring until thickened into a smooth béchamel sauce. Fold in chopped shrimp, lemon juice, parsley, salt, and pepper. Cook 2-3 minutes until mixture thickens further. Transfer to a bowl and cool completely, about 20 minutes.
04 - Roll dough on floured surface to 1/8 inch thickness. Using a 3-inch round cutter, cut circles. Place 1 teaspoon cooled filling in center of each circle. Fold dough over to form half-moon shape and press edges firmly to seal. Crimp edges with fork tines for secure closure.
05 - Place beaten eggs in shallow bowl and breadcrumbs in another. Dip each filled turnover in egg, allowing excess to drip off, then coat thoroughly with breadcrumbs. Press gently to adhere crumbs. Transfer to parchment-lined baking sheet.
06 - Pour vegetable oil into deep fryer or heavy-bottomed pot to depth of 3 inches. Heat to 350°F. Fry rissois in batches of 4-5 for 2-3 minutes per side until golden brown and crispy. Use slotted spoon to transfer to paper towel-lined plate to drain excess oil.
07 - Arrange on serving platter and serve warm with lemon wedges. May also be served at room temperature.