The ultimate Irish steak sandwich recipe - Gluten-Free Heaven

Ingredients

• 2 Irish sirloin steaks (about 300g each)
• a splash of vegetable oil
• 2 onions (peeled, thinly sliced)
• 4 large field mushrooms (thickly sliced)
• 1 tbsp mayonnaise
• 1 tbsp gluten-free yeast extract
• 2 medium gluten-free ciabattas or baguettes
• English mustard (for spreading)
• salt and freshly ground black pepper
• 50 g butter
• 50 g gluten-free flour
• 1 tbsp English mustard
• 150 g medium cheddar cheese (grated)
• 150 ml gluten-free beer