In a blender, combine the eggs and milk. Add the flour and salt and mix on high speed until smooth, pausing once or twice to scrape down the sides of the blender with a rubber spatula.
Alternatively, combine the flour and salt in a large bowl. Push the flour aside to make a well in the center. Break the eggs into the center and pour in 3/4 cup of the milk. Whisk in a small circle in the middle of the well to blend the eggs and the milk. Whisking constantly, gradually draw in the flour until you have a thick mixture. Add another 3/4 cup milk. Whisk until the mixture forms a smooth batter
Strain the batter (to remove any lumps) into a quart-size measuring cup with a spout or a pitcher. Let the batter rest at room temperature for 30 minutes.
In a small saucepan over medium-high heat, melt the 6 Tbs. butter. Continue cooking the butter until it turns golden brown and has the aroma of toasted nuts, 3 to 5 minutes. Watch carefully and adjust the heat or move the pan around if necessary; the butter can quickly go from lightly browned to burned. Skim off any foam that rises to the top. Let thee butter cool slightly and then stir it into the batter. The batter should be the consistency of heavy cream; thin it with a little more milk, if needed.
To cook the crêpes: Have ready the batter, a small nonstick skillet or a crêpe pan, plenty of softened unsalted butter, a flexible, heatproof spatula, a cooling rack, and about 20 torn sheets of waxed paper to use as separators.
Set the skillet over medium-high heat and add about 1 tsp. butter. Heat the butter, swirling it in the pan, until it stops bubbling. Pour in enough batter to coat the bottom of the pan, about a scant 1/4 cup, depending on the size of the pan.
Quickly tilt the pan in all directions to spread the batter evenly over the bottom and a bit up the sides of the pan. Immediately pour any excess batter back into the remaining batter. (You can cut off the “tail” this step leaves once the crêpe has set.)
Cook until the center of the crêpe is set and the bottom is lightly browned, 1 to 2 minutes, depending on the size of the skillet. Give the pan a good shake (or use a spatula to dislodge the crêpe) and turn it over. Cook until the center is firm and the edges underneath are lightly browned, about 30 seconds. Transfer the crêpe to a cooling rack. Proceed with the remaining batter, adding more butter to the pan as needed. Once cool, stack the crêpes between the sheets of waxed paper.