Step 1: Prepare the Spinach Base

1. Preheat Oven and Prepare Baking Sheet: Preheat your oven to 180°C (350°F). Line a large baking sheet (approximately 15×10 inches) with parchment paper. Ensure the parchment paper extends slightly over the edges to make it easier to lift the roulade later. Lightly grease the parchment paper with cooking spray or a little oil to prevent sticking. This pre-preparation is crucial for a smooth baking and removal process.
2. Cook the Spinach: In a large skillet or pot, add the fresh spinach. You don’t need to add any extra water as the moisture clinging to the leaves after washing is sufficient. Cook over medium heat, stirring occasionally, until the spinach wilts completely. This usually takes only 2-3 minutes. Overcooking will make the spinach mushy and less vibrant. The goal is just to wilt it down.
3. Drain Excess Moisture: Once the spinach is wilted, immediately transfer it to a fine-mesh sieve or colander. Press down firmly with the back of a spoon to squeeze out as much excess moisture as possible. This step is absolutely critical. Excess water in the spinach will make the roulade base too wet and it might not set properly. You want the spinach to be quite dry. You can even gently pat it dry with paper towels after squeezing.
4. Finely Chop the Spinach: Transfer the squeezed-dry spinach to a cutting board and finely chop it. Chopping the spinach ensures a smoother texture for the roulade base and makes it easier to incorporate with the other ingredients. Don’t skip this step, even if you used baby spinach.
5. Combine Spinach Base Ingredients: In a large mixing bowl, combine the chopped spinach, eggs, all-purpose flour, grated Parmesan cheese, garlic powder, salt, and black pepper. Mix thoroughly until all ingredients are well combined and you have a homogenous, slightly thick batter. Ensure there are no clumps of flour and the spinach is evenly distributed.

Step 2: Bake the Spinach Roulade Base

1. Spread Spinach Mixture Evenly: Pour the spinach mixture onto the prepared baking sheet. Using a spatula or the back of a spoon, spread the mixture evenly into a thin, rectangular layer, filling the entire baking sheet. Aim for an even thickness to ensure uniform baking and prevent thin spots from tearing when rolling. The thinner and more even the layer, the easier it will be to roll later.
2. Bake Until Set: Bake in the preheated oven for 12-15 minutes, or until the spinach base is set and lightly golden around the edges. It should spring back lightly when gently touched. Avoid overbaking, as this will make the roulade base dry and brittle, making it difficult to roll without cracking. Keep a close eye on it towards the end of the baking time.
3. Cool Slightly: Once baked, remove the baking sheet from the oven and let the spinach base cool slightly on the baking sheet for about 5-10 minutes. This allows it to firm up a bit and become easier to handle. Don’t let it cool completely on the baking sheet, as it might stick.

Step 3: Prepare the Smoked Salmon Filling

1. Soften Cream Cheese: While the spinach base is cooling, prepare the filling. Ensure the cream cheese is softened to room temperature. This makes it easier to mix and spread smoothly. If it’s still cold, microwave it in short 5-10 second intervals until softened, being careful not to melt it.
2. Combine Filling Ingredients: In a medium mixing bowl, combine the softened cream cheese, thinly sliced smoked salmon, finely chopped fresh dill, and fresh lemon juice. If using, add the horseradish cream now. Mix gently but thoroughly until all ingredients are well combined and the smoked salmon is evenly distributed throughout the cream cheese mixture. Be careful not to overmix, which can make the cream cheese watery.

Step 4: Assemble the Roulade

1. Loosen Spinach Base: Gently loosen the edges of the spinach base from the parchment paper using a spatula or knife. Be careful not to tear it.
2. Invert onto Parchment Paper: Carefully invert the spinach base onto a fresh sheet of parchment paper or a clean kitchen towel. Gently peel off the parchment paper that it was baked on. If it sticks in places, use a damp cloth to gently loosen it.
3. Spread Filling Evenly: Spread the prepared smoked salmon cream cheese filling evenly over the spinach base, leaving a small border (about 1 inch) at one of the longer edges uncovered. This uncovered edge will help seal the roulade when rolling.
4. Roll the Roulade: Starting from the filled long edge opposite the uncovered border, carefully roll up the spinach base tightly, jelly-roll style, using the parchment paper or towel to help guide and shape it. Roll firmly but gently to create a compact roulade without breaking the spinach base.
5. Wrap and Chill: Once rolled, wrap the roulade tightly in plastic wrap. Chill in the refrigerator for at least 2-3 hours, or preferably overnight. Chilling allows the roulade to firm up, making it easier to slice and serve, and allows the flavors to meld together beautifully.

Step 5: Serve and Garnish

1. Unwrap and Slice: When ready to serve, remove the roulade from the refrigerator and unwrap it. Place it on a cutting board. Using a sharp, serrated knife, trim off the ends of the roulade (these ends might be less neat). Then, slice the roulade into 1-inch thick slices. For clean slices, wipe the knife clean between cuts, especially if the filling is soft.
2. Arrange and Garnish: Arrange the roulade slices on a serving platter. Garnish generously with caviar or salmon roe and fresh dill sprigs. Serve immediately, or keep chilled until ready to serve.
3. Serve with Accompaniments: Offer lemon wedges alongside for guests to squeeze over their roulade slices if desired. Crackers, baguette slices, or cucumber rounds can also be served as accompaniments if you wish to make it a more substantial appetizer.