Soak currants in cognac for 3 hours.
Dissolve yeast in the warm water. Melt butter. Combine yeast, melted butter, sour cream, vanilla, eggs, and egg yolks. Sift together flour, sugar, and salt, add to yeast mixture, and stir until well blended. Knead on a floured board until smooth and elastic. Place in a buttered bowl, cover, and allow to rise in a warm place until doubled in bulk, about 1 to 1 1/2 hours.
In a large, heavy skillet, melt butter for the poppy-seed filling. Add poppy seeds and saute or a few minutes. Transfer to a bowl and mix in the honey, lemon juice, and currants. Whip the egg whites until frothy. Add the sugar 1 tablespoon at a time and continue whipping until very stiff. Fold the egg whites into the poppy-seed mixture.
In another bowl, combine apricot lekvar and pistachios for the apricot filling.
Divide dough into four equal parts. On a floured board, roll each portion of dough into a large rectangle 1/4 inch thick. Spread poppy-seed filling evenly on two of the rectangles and the apricot filling on the other two rectangles, leaving a 1-inch margin on the two short sides and one long side of each. Wet the margins with water and roll up each rectangle, beginning with the edge that has no margin. Form each into a crescent, sealing the edges together, and place on parchment-lined baking sheets. Cover and allow to rise approximately 1 hour in a warm place.
Heat the oven to 350 degrees.
Brush the rolls with the egg glaze. Using a sharp knife, make slits in the top of each crescent. Bake for 45 to 60 minutes, until deep gold. Cool on a wire rack.
You can grind the poppy seeds in a food grinder or purchase them already ground in gourmet shops. Apricot lekvar is a rich apricot butter available in Hungarian food stores.