Start by cutting the beef into smaller pieces.
Next, transfer all the meat to the zip lock bag.
Pour in the beer, seal the bag and let everything marinate for 30 minutes.
After this time has passed, remove the beer, add the cornstarch and mix very well to combine.
In a medium-sized pan, add the butter, a drizzle of vegetable oil and stir until the butter is completely melted.
Add the meat and fry until it gets lightly golden brown.
Remove the meat, add the onions sliced into rings, the crushed garlic cloves, the green bell pepper sliced into strips and sauté.
Add the meat that we fried, season with the salt, a pinch of black pepper, the sweet paprika, the mustard and mix to combine the seasonings.
Next, add the water, mix again and let everything cook for 10 minutes.
After this time has passed, dissolve the cornstarch in the water, pour it into the pan and mix.
Add green onions to taste and mix again.
Serve.