Cook pasta as directed.
Melt butter in small saucepan. Add shallots and sauté over medium-high heat until fragrant and beginning to brown.
Lower heat to medium-low and add sour cream. Stir for 15 seconds and then add cream and feta. Stir until feta is completely melted.
Remove from heat and stir in parmesan.
Immediately toss sauce with drained pasta and serve warm.