When you combine the wet and dry ingredients, the butter will re-solidify as it cools, causing the dough to have a lot of lumps. Don't worry, it's completely normal and won't affect the taste or texture of the waffles. The butter will melt in the waffle iron. Yes, you can use rapeseed, vegetable oil, or butter.
If you use butter, make sure you don't raise the temperature above 375°F so that it doesn't burn. While waffles and pancakes have the same ingredients, they're slightly different doughs. Waffle dough is a little thicker and contains more sugar than pancakes. Here's a delicious homemade blueberry pancake recipe if you want to make pancakes.
To reheat the waffles, place them in the microwave for 30 seconds; if they are frozen, repeat the procedure. Then place them in the toaster until they are crisp on the outside again. This waffle recipe calls for all-purpose flour, but you can also use flour with yeast. If it does, just omit the baking powder and salt.