Place the salmon pieces in a deep, medium-sized skillet or shallow saucepan. Pour in enough boiling water to almost cover fish. Add lemon slices. Bring to a boil over high heat. Reduce heat to low, cover, and simmer 10 minutes, or until salmon is opaque in center when flaked. Remove salmon with a slotted spatula. Remove the skin and bones and flake fish into a medium bowl.
In a separate bowl, whisk together egg and milk. Add flour, baking powder, salt and pepper. Whisk just until blended. Pour batter over cooked salmon. Stir gently to mix.
Melt 3 tablespoons butter in a large skillet over medium heat. Pour batter, 1/4 cup for each latke, into the hot butter. Raise the heat to medium-high and cook latkes until nicely browned and crisp on bottom, about 4 minutes. Turn over and cook until second side is crisp and browned, about 2 minutes longer. Repeat in 1 or 2 more batches to use remaining batter, adding more butter as needed.
Drain on paper towels. Serve warm, with lemon wedges. Garnish with Cucumber and Red Onion Salad, if desired