In double boiler, melt the butter and chocolate and stir until smooth.
Whip the egg yolks and sugar until fluffy and pale in color.
Fold the butter/chocolate mixture into the egg yolk/sugar mixture, adding in the coffee liqueur.
Whip the egg whites to soft peaks and gently fold into the butter/chocolate/egg yolk/sugar mixture.
Pour into pie pan and back for 25-35 minutes then allow to cool completely.
Cajeta
In a medium sauce pan, bring water and sugar to a boil. Do not stir.
Remove from heat when the sugar is amber in color.
Add enough cream to thin the caramel to a fairly liquid consistency.
Stir in butter.
Test consistency by dipping a spoon into carmel mixture and allow to coat. If the cajeta is gooey but holds its shape, it is ready. If it hardens too much, add a little mroe cream, stir, and test again.
Bring it all together
Flip out the cooled cake on to a wire rack. Remove wax paper.