Step 1

Melt marshmallows in large microwave safe bowl in 30 second bursts until it can be stirred smooth. Stir in milk, set aside to cool a bit.

Step 2

Meanwhile beat the butter until it is smooth and creamy. Add the shortening and beat until combined.

Step 3

Add melted marshmallow mixture and mix well.

Step 4

Stir in powdered sugar, salt, meringue powder and vanilla. Mix on low for several minutes.

Step 5

Adjust the consistency with more milk or powdered sugar as needed.