Break chocolate into pieces and put in a microwave safe bowl. Add coconut oil and microwave for 30 seconds. Take it out of the microwave, give it a stir, then put it back in for a another 30 seconds. Remove from microwave and stir until the chocolate is fully melted and the sauce is smooth. If it needs longer, put it back in the microwave. Store in an airtight container at room temperature. You may need to heat sauce slightly before using if it has been a little while since you last used it. Pour on ice-cream and leave for 30 seconds until the sauce is hard.