Step 3: Pasta cooking and butter melting.
As soon as the water comes to a boil, dump your pasta in. You need to cook the pasta so that it is slightly underdone. You want it to still be able to accept some liquid so that it'll soak up the cream later!
Put the 6 tbs. of butter into the saute pan over medium/low heat and start it melting while the pasta cooks. As soon as it's melted, turn off the heat. You don't want the butter to brown.
When the pasta is done cooking, drain it and we'll move on to the next step.