In a skillet over medium heat add butter, olive oil and onions. Cook for 10-12 minutes until onions are soft.
Add garlic, salt, pepper, paprika, red pepper flakes and cook for 1 more minute.
Slowly stir in heavy cream and continue to stir for about 1 minute. Add spinach to the sauce and stir to coat. Let cook for another 4-5 minutes until spinach is completely cooked down. Remove from heat and stir in swiss cheese. Let sit for about 3-4 minutes to let the cheese melt.
Preheat oven to 400 degrees.
Place 2 tbsp of spinach dip on top of the sliced bread and set on a parchment paper lined baking sheet. Repeat with all slices, should be about 6.
Place in the preheated and bake for 10-15 minutes until bread is nice and toasted and tops are lightly golden. Enjoy!