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1
Preheat your oven to 400 degrees F and position the rack to the center of the oven.
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2
Lightly butter a 7-inch springform pan and line with parchment: dust the sides with flour and tap out an excess.
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3
In a double-boiler, melt the chocolate over simmering water; remover from heat and stir until cooled.
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4
In a stand mixer fitted with the paddle attachment, beat the butter using medium-high speed until smooth, about 1 minute.
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5
Switch to low speed, beat in the powdered sugar, then return to medium-high, and beat until fluffy and lighter in color and texture, about 2 minutes.
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6
Beat in the egg yolks first, one at a time, scraping down the sides of the bowl; beat in the chocolate and the vanilla.
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7
In another large bowl, beat the egg whites with the castor sugar, using high speed, until they form soft, shiny peaks.
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8
Stir 1/4 of the egg whites into the chocolate mixture, then fold in the remaining, leaving some strips of white showing.
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9
Sift half the flour over the sugar, then fold in; repeat with remaining flour.
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10
Spread the batter evenly into the prepared pan and bake until a wooden toothpick inserted into the center comes out clean, about 45 minutes.
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11
Cool on a wire rack for 10 minutes, then remove the sides of the springform pan and invert the cake onto the rack, remove the paper and re-invert to turn right side up and let cool completely.
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12
Use a serrated knife to trim the top of the cake to make it level; cut the cake horizontally to make two even layers.
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13
Place the bottom layer on an 8-inch cardboard cake round; brush the top of the layer with half the warm apricot glaze.
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14
Place the second layer on top, then brush with the remaining glaze; transfer the cake to a wire rack that has been set over a jellyroll pan (to catch drips) and let the glaze set.
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15
Pour the warm chocolate glaze over top and use an offset spatula to gently spread the glaze all over, including the sides, so that the cake is completely covered; use any glaze that drips to patch missed spots.
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16
Once glaze has begun to set, place cake on a serving platter and cool completely in the refrigerator at least an hour; let the cake stand at room temperature 1 hour before serving.
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17
If desired, serve with a saucer of unsweetened whipped cream for dipping.
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18
For the apricot glaze: In a small saucepan, bring the preserves and rum (or water) to a boil over medium heat, stirring often; cook, stirring, until very sticky and does not easily leave the spoon, 2 to 3 minutes. Strain through a wire sieve, pressing on the solids. Use warm.
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19
For the chocolate glaze: In another small saucepan, heat the sugar, water, and chocolate to a boil over medium-high heat, stirring occasionally. Reduce the heat to medium and cook, uncovered, stirring, until it reaches 234 degrees F on a candy thermometer, about 5 minutes. Remover from heat and stir to cool for about 1 minute. Use immediately and do not scrape the pan (the chocolate that clings to the saucepan will not be a glaze, it is too thick).
