Baked Hawaiian Sandwiches

I saw a recipe on All Recipes for Baked Hawaiian Sandwiches. I made another version awhile back, but can't seem to locate the recipe. So, I used the following recipe, but made adaptations based on what I remember.

The recipe is for 24 sandwiches, but only 20 would fit into a 9"x13" pan that I used (versus the cookie sheet that is recommended. Having made this recipe before, I didn't want any sauce dripping onto the bottom of the oven. Thus, my preference for the 9"x13" pan.

At any rate, I kept the amount of ingredients the same, just altered the number of rolls used. To make the sandwiches, you'll need:

20-24 Hawaiian bread rolls (such as King's®), split
12 thin slices of honey-cured deli ham, halved (I used 24 slices since I wasn't using turkey)
12 slices Swiss cheese, halved (I used a 7-ounce package with 11 slices that I cut in half and then folded in half1)
12 thin slices deli smoked turkey, halved (I didn't use this)
12 thin slices provolone cheese, halved (I didn't use this)
1/2 cup butter
1/4 cup white sugar
1/4 cup dried onion flakes
2 tablespoons poppy seeds (I used 1 tablespoon poppy seeds because I ran out...but would use more next time)
1 tablespoon honey mustard (I used 1 tablespoon of hot-sweet mustard plus 1/2 tablespoon of honey)
Horseradish sauce (this isn't on the All Recipes recipe, but I remember using it in the original version that I made)

To make the sandwiches, you'll need to preheat the oven to 400 degrees F (200 degrees C).

Line a 9"x13" pan or cookie sheet with parchment paper to keep the bottoms from burning.

Arrange bottom halves of Hawaiian rolls on a baking sheet. Spread horseradish sauce on the rolls. Place a half slice each of ham, Swiss cheese, smoked turkey, and provolone cheese onto each roll bottom. Place top halves onto each bottom to make sandwiches.

Melt butter in a saucepan over low heat and stir in sugar, dried onion flakes, poppy seeds, and honey mustard until mixture is smoothly combined, creamy, and the sugar has dissolved, about 2 minutes.

Brush over the tops of each sandwich. (The rolls on the top are for Olivia since she doesn't like onions or horseradish sauce. Note: if no sauce will be on top of the rolls, they can be baked for a shorter period of time so that the bread doesn't get too overbaked.)

Bake sandwiches on the preheated oven's lower rack until tops are golden brown and fillings are hot, about 15 minutes.

This was the recipe that Sophia and Olivia requested for their back-to-homeschool meal. We also had baked beans, salad, orangeade, and orange creamsicle cookies for dessert.