In a large saucepan, cook 3/4 cup butter over medium-high heat, stirring constantly, until boiling. Whisk in brown sugar and cook just until mixture begins to brown. Reduce heat to medium-low, add marshmallows and stir just until marshmallows are mostly melted. Remove from heat and stir in vanilla, almonds and Cheerios™. Press into an 9 x 11” nonstick baking pan.