Cook egg noodles according to package directions and drain.

Melt butter in a large skillet over medium heat.

Add onion to the skillet and cook until softened.

Add portobello mushrooms to the skillet and cook until softened. Remove from heat and set aside.

In a separate large skillet, heat vegetable broth over medium-high heat until it reduces to about 1/3 of its original volume.

Add the cooked mushrooms to the reduced vegetable broth and reduce heat to low.

In a separate bowl, whisk together sour cream and flour until smooth.

Gradually add the sour cream mixture to the mushroom mixture in the skillet, stirring constantly.

Cook on low heat until the sauce thickens, being careful not to boil or curdle the sour cream.

Serve the stroganoff sauce over the cooked egg noodles.

Garnish with fresh parsley before serving.