Add butter to a microwave-safe bowl and microwave for 30 seconds to melt the butter.
Add the room temperature (or warmer - see my notes on why this is important!) cream cheese to the bowl, and microwave again for about 20 seconds.
Stir in powdered sugar and vanilla until the glaze is thoroughly mixed. It should be runny enough to drizzle onto the cake at this point, but if it's not, just zap it in the microwave for an additional 15 seconds or so - just until the glaze is runny enough to drizzle over the cake.
Using a spoon, drizzle the glaze evenly over the cake, and if you wish, top with some extra chopped pecans for garnish.
Allow cake to fully cool before placing a lid/cover over it. You can store the cake on the counter overnight, but if you're storing it for more than a day, keep it in the fridge - the pumpkin in the cake causes it to spoil faster if you don't refrigerate it.
To make this extra special, serve with some homemade whipped cream or vanilla ice cream! YUM!