Place chocolate in a microwave-safe glass or ceramic bowl. Melt in the microwave in 15-second intervals, stirring after each heating, 1 to 3 minutes.
Beat sugar and butter together in a bowl using an electric mixer until fluffy. Add the melted chocolate. Blend in eggs 1 at a time. Add pecans and vanilla extract. Pour mixture into the prepared crust. Cover with plastic wrap and refrigerate until set, at least 24 hours.