Preheat oven to 325 degrees F.
Butter and flour muffin tin or 6-8 ramekins depending on the size you want to make. I use silicone baking cups and they work great!
In a small saucepan over low heat, melt butter, chocolate and espresso powder, stirring until melted and smooth.
In the bowl of an electric mixer, beat the eggs, vanilla and sugar until light and fluffy, a couple of minutes on high. Slowly drizzle the melted chocolate into the egg mixture and stir until incorporated.
Divide the batter evenly among the cups and bake for about 15 minutes, until just set. Cool and then refrigerate the cakes in their cups until well chilled.
Make the glaze. In a small saucepan over low heat, bring the cream to a simmer. Add the chocolate, butter and espresso powder and stir until melted and completely smooth. Allow the glaze to cool a bit before pouring onto the cakes.
Remove the cakes from their cups and invert onto a sheet pan with a rack. Spoon glaze over the cakes and spread evenly around the sides and top. Allow to set before serving.