Step 1
First make the fondant. It needs to be refrigerated overnight before using. To make the fondant you'll need a marble slab or a baking sheet and an offset spatula to fold the candy. If you're using a baking sheet rinse it with water leaving a few drops on the pan.
Step 2
Dissolve the cream of tarter in the water in a heavy-bottomed saucepan. Add the sugar and bring the mixture to a boil over medium-high heat. Swirl the pan occasionally to help dissolve the sugar. Do not stir once the sugar syrup begins to boil. Heat to 240 degrees F (115 degrees C) or until a small amount of syrup dropped into cold water forms a soft ball that flattens when removed from the water and placed on a flat surface.
Step 3
Immediately pour the candy onto the baking sheet or marble slab and let cool for 10 minutes. Use a spatula to vigorously knead the candy folding it over itself. Knead until it begins to look cloudy 5 to 10 minutes; allow it to cool. Transfer the fondant to a heatproof bowl or the top of a double boiler. Refrigerate overnight.
Step 4
To make the sponge dissolve the yeast and 1 teaspoon sugar in 1/4 cup of the room-temperature milk. Pour the remaining 1/2 cup milk into the bowl of a stand mixer. Add 1 cup of flour and the yeast mixture. Mix with a fork to combine. Cover the bowl with a towel and allow to rest until bubbly 10 to 15 minutes.
Step 5
Stir the remaining 3 cups of flour 1/4 cup sugar salt room-temperature eggs and zest from 1 lemon into the sponge. Use the dough hook to mix the dough on the lowest setting. Mix the dough for about 5 minutes occasionally scraping the dough off of the hook and down the sides of the bowl.
Step 6
Increase the speed to medium-low and add the softened butter 1 tablespoon at a time until fully incorporated. Allow the dough to mix for an additional 5 minutes scraping the dough down as needed. Add the ground almonds and turn the mixer on for 1 or 2 turns mixing just until incorporated. Transfer the dough to a lightly floured work surface and shape it into a ball. Place the ball in an oiled mixing bowl and cover with plastic wrap and a kitchen towel and let it rise until doubled 1 1/2 to 2 hours.
Step 7
While the dough is rising prepare the filling. Heat the milk in a heavy 4-quart saucepan until it begins to boil; stir in the butter and sugar. Remove the pan from the heat and add the poppyseeds 1 1/2 teaspoons of lemon zest and the cinnamon. Let the mixture stand for 30 minutes to soften the poppyseeds. When the mixture is cool whisk in the egg.
Step 8
Punch down the dough and roll it out into a 10 1/2- by 16-inch rectangle. Spread the filling evenly over the dough leaving a 1-inch margin on all sides. Roll the dough up into a log starting with the long side and pinch the edges together to form a seam. Place the loaf seam-side down on a parchment-lined baking sheet. Cover it with greased plastic wrap or a well-floured kitchen towel and allow it to rise for an additional 30 to 40 minutes.
Step 9
Preheat an oven to 400 degrees F (200 degrees C).
Step 9
Bake the stollen until golden brown on the bottom of the loaf about 40 minutes. Let the bread cool completely before glazing.